Responsorial chants - Chants sung by alternating soloist and choir.

Direct chants - Chants sung without alternation.

Syllabic chants - Chants in which most or all of the syllables have a single note each.

Melismatic chants - Chants which include long melodic pasages on a single syllable.

Neumatic chants - Chants which are otherwise syllabic but have occasional short melismas of four or five notes on some syllables.

Neumes - Notes in Gregorian notation.

Modern Gregorian notation - The staff is four lines, one of which is designated by the clef as either c'² or f, although these clefs do not indicate abolute pitches - they are only relative. All notes have essentially the same duration, regardless of shape. A dot after a neume doubles its value. Two or more neumes in succession on the same line or space, if on the same syllable, are sung as though tied. A horizontal dash above a neume means it should be slightly lengthened. Composite neumes (single signs representing two or more notes) are to be read from left to right in the normal manner, except for the podatus or pes (looks like backward C kind of - there is no left to right since the "notes" are exactly vertical to each other), in which case the lower note is sung first. An oblique neume indicates only two different notes (not a portamento). A neume never carries more than one syllable, even if it's composite. Flat signs, except in a signature at the beginning of a line, are valid until the next vertical division line or until the beginning of the next word. The little sign at the end of a line is a guide to show the position of the first note in the following line. An asterisk shows where the chorus takes over from the soloist.  The signs ij and iij indicate that the preceding phrase is to be sung twice or three times respectively.

Recitation tones - Chants for the recitation of prayers and readings from the Bible.

Reciting note - (a.k.a. tenor or dominant) Recitation tones and psalm tones are chanted almost exclusively on and around a single "reciting" note, usually a or c'.

Psalm tones - Standard formulas, similar to recitation tones, but slightly more complex.  There is one tone for each of the eight church modes and an extra one, called the Tonus peregrinus or "foreign tone." The psalm tones have been taken directly from chants of the Hebrew synagogues. A psalm tone consists of the initium (used only in the first verse of the psalm), tenor, mediatio, and terminatio. Usually the last verse of a psalm is followed by the Lesser Doxology, which ends et in secula seculorum, Amen ("world without end, Amen" - abbreviated in texts with the vowels of the last two words: euouae) or the Gloria Patri ("Glory be to the Father").

Initium - a two or three-note introductory formula that leads to the reciting note in reciting chants or to the tenor in psalm tones.

Mediatio - A semicadence in teh middle of the verse of a psalm.

Terminatio - The final cadence of a psalm.

Biblical prose texts - Texts which come from prose sections of the Bible. Examples: the lessons of the Office, the Epistle and Gospel of the Mass.

Epistle - A chant or recitation whose text comes from one of the Epistles of the New Testament.

Gospel - A chant or recitation whose text comes from one of the four Gospels of the New Testament.

Biblical poetical texts - Texts which come from poetic sections of the Bible. Examples: the psalms and canticles.

Canticle - A chant whose text comes from The Song of Songs or Song of Solomon, one of the books of the Old Testament.

Psalm - A chant whose text comes from the Book of Psalms, one of the books of the Old Testament.

Non-Biblical prose texts - Prose texts which do not come from the Bible. Examples: Te Deum, many antiphons, including three of the four Marian antiphons (see below).

Antiphons - The most numerous kind of chant. Many employ the same melody-type, making only slight variations to accommodate the text. Antiphons were originally intended for a group of singers rather than a soloist and the older ones are usually syllabic or only slightly florid with stepwise melodic movement, limited range and a comparitively simple rhythm.

Non-Biblical poetical texts - Poetic texts which do not come from the Bible. Examples: Hymns and sequences.

Hymn - A chant whose text comes from a non-Biblical poetic source. Usually strophic (each verse sung to the same melody).

Mass – The principal service of the Catholic Church. Its liturgy was actually developed later than that of the Offices. The word “Mass” comes from the service’s closing phrase: Ite missa est (“Go, [the congregation] is dismissed”). This service is known in other Christian churches as the Eucharist, the Liturgy, Holy Communion and the Lord’s Supper. The culminating act of the Mass is the commemoration or re-enactment of the Last Supper (Luke 12:19-20; 1 Cor. 2:23-26).  In the Catholic Church, there are two forms of the Mass: High Mass (Missa Solemnis) and Low Mass (Missa Privata).  The historically settled form of the Mass proceeds as follows:

First Main Division: Introit, Kyrie, Gloria (except during the penitential seasons: Advent and Lent), Collects (prayers), the reading of the Epistle, the Gradual, the Alleluia (during penitential seasons is replaced by the Tract), the reading of the Gospel, the Credo, a sermon (if any).

Eucharist proper: During the preparation of the bread and wine - the Offerty. Then: various prayers, Preface, Sanctus, Benedictus, Canon, Pater noster, and Agnus Dei.

After the bread and wine have been consumed: Communion, the singing of the priest’s Post-Communion prayers and the service is concluded by the dismissal formula Ite missa est or Benedicamus Domino.

Ordinary of the Mass (Ordinarium missae) – The invariable parts of the service, which include the Kyrie, Gloria, Credo, Sanctus, Benedictus and Agnus Dei.  All of these parts are sung by the choir, although in early Christian times they were also sung by the congregation.  Typically, since the 14th Century, these are the texts most often set to music and if a composer wrote a mass, it is a setting of these sections, although many of the best known of these settings are not appropriate for actual liturgical use. Originally, these chants were all probably quite simply syllabic melodies sung by the congregation. These were replaced, after the ninth century, by other settings. Except for the Gloria and the Credo, which remained mainly syllabic, the other chants of the Ordinary are now more ornate.

Proper of the Mass (Proprium missae) – The variable portions of the mass or rather, the parts that change according to the season of the year or the dates of particular feasts or commemorations.

Requiem Mass (Mass for the Dead) – A special Mass, so called from the first word of its Introit, which begins Requiem aeternam dona eis Domine (“Grant them eternal rest, O Lord”). This mass has its own Proper, which does not vary with the calendar, the Gloria and Credo are omitted and the sequence Dies irae, dies illa (“Day of wrath, O dreadful day”) is inserted after the Tract.  As a result, modern settings of the Requiem usually include certain texts of the Proper, such as the Introit, the Offertory Domine Jesu Christe, the Communion Lux aeterna (“Light eternal”) and sometimes the Responsory Libera me, Domine (“Deliver me, O Lord”).

Introit – Part of the Proper of the Mass. Originally this was an entire psalm with its antiphon, chanted during the entrance of the priest. Later, it was shortened to include only the original antiphon, a single psalm verse with the customary Gloria Patri and the repetition of the antiphon.

Kyrie – Part of the Ordinary of the Mass. Sung to the Greek words Kyrie eleison, Christe eleison, Kyrie eleison (“Lord have mercy upon us, Christ have mercy upon us, Lord have mercy upon us”) with each invocation being sung three times. This naturally suggests a three-part sectional arrangement, often ABA or sometimes ABC, with C motivically related to A. Often A and B are similar in outline and have identical final phrases, and the last repetition of part C is sometimes expanded.

Gloria – Part of the Ordinary of the Mass. Begun by the priest with the words Gloria in excelsis Deo (“Glory be to God on high”) and continued by the choir from Et in terra pax (“And on earth peace”)

Gradual – Part of the Proper of the Mass. Sung by a soloist or soloists with responses by the choir. In the modern chant books, the Gradual is a shortened responsory, with an introductory refrain or respond, followed by a single verse of the psalm. The refrain is begun by the soloist and continued by the choir. The verse is sung by a soloist with the choir joining in on the last phrase.

Alleluia – Part of the Proper of the Mass. Sung by a soloist or soloists with responses by the choir. Replaced by the Tract during Advent and Lent.  Alleluias consist of a refrain on the single word "alleluia" and a verse, followed by repetition of the refrain. Customarily, the soloist sings the word "alleluia" which the chorus repeats and continues with the jubilus. Then, the soloist sings the verse with the chorus joining on the last phrase, after which the entire "alleluia" with jubilus is sung by the chorus. The "alleluia" is moderately florid and the jubilus, of course, is melismatic. The verse usually combines shorter and longer melismas. Often, the last part of the verse repeats part or all of the refrain melody. Within the general scheme, the melody is often organized by the repetition or echoing of motives, musical rhyme, systematic combination and contrast of melodic curves and similar music-related organizational devices, helped in their development by the fact that in an Alleluia there is a great deal of melody without words and there was felt a need for purely musical principles of order in the chant.

Jubilus - A long melisma on the final "ia" of "alleluia" in an Alleluia.

Tract – Part of the Proper of the Mass. More solemn than the Alleluia which it replaces during Advent and Lent, this is sung by a soloist or soloists with responses by the choir as well. Tracts are the longest chants in the liturgy.  They are all in either the second (Hypodorian) or eighth (Hypomixolydian) mode. Tracts in second mode have for their texts words of penitence and sadness. Those in eighth mode are set with texts of hope and assurance. Each verse of the Tract is divided by a mediatio as in a psalm tone and the characteristic reciting notes or tenors of psalmody are present. There are also certain recurring melodic formulas found in many different Tracts and regularly in the same place in the form, suggesting they are a surviving elaborated form of music from Gregorian times or earlier.

Credo - Part of the Ordinary of the Mass. Begun by the priest with Credo in unum Deum (“I believe in one God”) and continued by the choir from Patrem omnipotentem (“the Father Almighty”).

Offertory – Part of the Proper of the Mass. Sung during the preparation of the bread and the wine. Originally, they were very long chants sung by both congregation and clergy during the ceremony of presentation of bread and wine. This has since been shortened. Possibly, some of the text repetitions that appear in Offertories were optional, so that singers could adjust the length of the chant according to the time required for the presentation of the offerings.  Offertories show some of the same musical organization techniques as Alleluias. The melismas of Offertories are closely related to the text, serving an expressive as well as a decorative purpose.

Preface – Part of the Proper of the Mass. Leads into the Sanctus.

Sanctus – Part of the Ordinary of the Mass. “Holy, holy, holy” sung by the choir. Similar to the Kyrie and Agnus Dei, the Sanctus is divided into three sections. Text: Sanctus, sanctus, sanctus ("Holy, holy, holy"), Pleni sunt caeli et terra ("Heaven and earth are full"), Benedictus qui venit ("Blessed is He that cometh").

Benedictus – Part of the Ordinary of the Mass. “Blessed is He that cometh” sung by the choir.  (Also see Sanctus).

Canon – the prayer of consecration.

Pater noster – the Lord’s prayer.

Agnus Dei – Part of the Ordinary of the Mass. “Lamb of God”. Text: "Agnus Dei ... miserere nobis" ("Lamb of God ... have mercy upon us"), Agnus Dei ... miserere nobis, Agnust Dei ... dona nobis pacem ("Lamb of God ... grant us peace"). Musically, the Agnus Dei may have the form ABA or be organized in ways similar to the Kyrie, although sometimes the same music is used for all sections.

Communion – Part of the Proper of the Mass. Sung by the choir after the bread and wine have been consumed. A short chant, often consisting of only one verse of Scripture, usually of a quiet or reverent character.

High Mass – The form of the Catholic Mass that includes considerable chanting by a Celbrant, a Deacon, and Subdeacon, along with chanting or polyphonic singing by the choir and/or congregation.

Low Mass – A shortened and simplified form of the Mass in which one priest (Celebrant) takes over the parts previously assigned to the Deacon and Subdeacon, and a server takes the part of the choir and all other assistant ministers.

Offices (a.k.a. Canonical Hours) – One of the two principal classes of services in the historical Catholic Latin liturgy. There are 8 offices, which are celebrated every day at stated times: Matins (before daybreak), Lauds (at sunrise), Prime, Terce, Sext and Nones (respectively at about 6 A.M., 9 A.M., noon and 3 P.M.), Vespers (at sunset) and Compline (usually immediately after Vespers). The principal features of the Offices are the chanting of psalms with their antiphons, the singing of hymns and canticles, and the chanting of lessons (passages of Scripture) with their responsories.  Musically, the most important Offices are Matins, Lauds and Vespers (before daybreak, sunrise and at sunset).

Matins – The Office (or Canonical Hour) that is celebrated before daybreak. It includes some of the most ancient chants of the Church.

Vespers – The Office (or Canonical Hour) that is celebrated at sunset. It has the canticle Magnificat anima mea Dominum (“My soul doth magnify the Lord,” Luke 1:46-55).  This Office is the only one that admitted polyphonic singing from early times.

Compline – The Office (or Canonical Hour) that is celebrated immediately after Vespers (which in turn is celebrated at sunset). A feature of this Office is the singing of the four antiphons of the Blessed Virgin Mary (a.k.a. the “Marian” antiphons) – one for each of the main divisions of the Church year

Alma Redemptoris Mater (“Sweet Mother of the Redeemer”) – The antiphon of the Blessed Virgin Mary which is sung during the Office of Compline from Advent to February 1.

Ave Regina caelorum (“Hail, Queen of the Heavens”) – The antiphon of the Blessed Virgin Mary that is sung during the Office of Compline from February 2 to Wednesday of Holy Week.

Regina caeli laetare (“Rejoice, Queen of Heaven”) – The antiphon of the Blessed Virgin Mary that is sung during the Office of Compline from Easter to Trinity Sunday.

Salve Regina (“Hail, O Queen”) – The antiphon of the Blessed Virgin Mary that is sung during the Office of Compline from Trinity until Advent.

Graduale - The liturgical book that holds the Gregorian music for the Mass (both Proper and Ordinary).

Antiphonale (a.k.a. Antiphonal) – The liturgical book in which the Gregorian music for the Offices is collected.

Liber Usualis - Another book of Gregorian music which contains a selection of the most frequently used chants from both the Antiphonale and the Graduale.