Performing editions: These are the scores that you'll find on the 2nd floor of MPAL. They have been edited by publishers and teachers/performers to include fingerings, phrasing, and sometimes tempo indications. These editions range in quality, but you'll find that publishers such as Henle, Wiener Urtext, Breitkopf and Hartel (among others) tend to put out better editions than, for example, International.
Collected editions/critical editions: These are sets of composers' collected works. They have been compiled by scholarly editors to try to give the closest indication of what the composer truly intended. Critical commentary is included that discusses any alterations in accidentals, notes, ornaments, and so forth. The editors refer to any manuscript sources available and also research whether the composer later made changes (such as notes or cuts, etc.). These editions are also sometimes called ‘complete editions’ or ‘Gesamtausgabe’.
Monuments or Denkmäler: Are collected editions that focus on a particular country, region, or type of music rather than a single composer.
See "Editions, historical." article in Oxford Music Online for a more complete definition. For common abbreviations of larger Denkmäler (e.g., DTO is Denkmäler der Tonkunst in Ö̈sterreich) see the abbreviations list in Grove (Oxford Music Online > Tools & Resources > Abbreviations and Library Sigla > Bibliographical Abbreviations).
Autograph: manuscript written in the hand of a particular person; in normal musical parlance, the manuscript of a work in the hand of its composer
Briefe: Letters (correspondence)
Buhnenwerke: Stage works
Faksimile: exact copy (usually of a manuscript)
Holograph: sometimes used to distinguish a manuscript wholly in the hand of its author or composer
Kammermusik: chamber music
Klaviermusik: piano music
Kirchenmusik: church music
Kritischer bericht: critical commentary
Literatur: articles/studies about work
Manuscript: source that is written by hand
Mehrstimmige Gesange: Songs for multiple voice parts
Opera Omnia: all works
Opus Zahl: Opus (work) number
Orchesterwerke: Orchestral works
Oeuvres completes: complete works
Reihe: Row or series
Thematisches-Verzeichnis: thematic catalog, inventory
Urtext: intended to reproduce the original intention of the composer as exactly as possible, without any added or changed material
Vergleiche (Vgl.): see also, compare
Widmung: dedication (gewidmet= dedicated to)