Antiphon: A short chant used for the Mass or Liturgy of the Hours, usually derived from the Bible but sometimes composed in praise of a saint.
Canticle: A hymn or other chant that is based on a Biblical text.
Codex: A medieval book (a manuscript consisting of leaves bound together as opposed to a scroll or single leaf).
Collect: A short liturgical prayer including an invocation and plea.
Fragment: A leaf, group of leaves, or part of a leaf that once belonged to a larger codex.
Historiated: A historiated initial contains identifiable figures (people, objects, etc.) that typically have some relationship to the text.
Hymn: A multi-stanza religious poem in regular meter set to music; the melody is repeated for each stanza.
Illumination: Any drawing in a medieval manuscript. While many “illuminated” manuscripts are very plain, the term itself refers to the gold leaf that is used in some illuminations.
Initial: The first letter of a particular text; in medieval manuscripts, initials are often decorated.
Leaf: An individual page from a codex.
Liturgy of the Hours/Divine Office: Specific prayers recited on the seven daily canonical hours.
Manuscript: any document written by hand (as opposed to printed), from Latin manu (by hand) + scriptus (written).
Ordinary: Parts of the Mass or Liturgy of the Hours that are consistent throughout the Catholic liturgical year (as opposed to the proper, which includes chants sung on specific feast days).
Parchment: Prepared animal skin on which the majority of medieval manuscripts were written (vellum is high-quality parchment made from calf skin, preferred in France).
Recto: The front side of a leaf (on the "right" side when you are paging through the codex).
Rubric: Instructions (usually in red) for when the chants in a liturgical manuscript should be performed.
Verso: The back side of a leaf (on the "left" side when you are paging through the codex).