Mendelssohn: String Octet, MWV R 20, Op. 20

Choral Score
A score for vocalists that only contains the vocal lines. The instrumental parts are not there for reference. Generally, cheaper than a vocal score and requires multiple copies for purchase.

Facsimile of the Autograph
These are hardcover, research-quality reproductions of the original hand-written scores from the composer.

Hardcover
Some publishers print a hardbound, linen-covered version in addition to the standard paperback. The music inside is identical. These editions are beautiful though rarely cheap.

Orchestral Parts
Similar to a wind set, this is a collection of parts. In the case of strings, the numbers listed are the number of copies included, though generally these are available individually (often with minimum quantities required).

Paperback
When publishers offer multiple bindings (e.g. hardcover) or study scores, this is the "standard" version. If you're planning to play the music, this is probably what you want.

Performance / Playing Score
For chamber pieces, playing scores have all of the parts on one system. There are not separate parts for each player.

Score (Full Score)
For ensemble music, this indicates that the edition contains all parts on a single system (there are not separate parts for each player). In larger ensembles, this is for the conductor.

Set of Parts
For ensemble music, this indicates that there are separate parts for each player.

Solo Part with Piano Reduction
For solo pieces with orchestra, this is a version that contains a piano reduction of the orchestra parts. For piano pieces, two copies are typically needed for performance.

Study Score
A small (think choral size) copy of the complete score meant for studying, and not playing. They make great add-ons when learning concertos and small chamber works.

Vocal Score
A score prepared for vocalists that includes the piano/organ part or a reduction of the instrumental parts.

Wind Set
For orchestral music, this is a collection of wind and percussion parts. The specific quantities of each instrument are notated.

With Audio
In addition to the printed music, the edition contains recordings of the pieces. This may be an included CD, or access to files on the internet.

With / Without Fingering (Markings)
Some publishers prepare two copies - a pure Urtext edition that includes no fingering (or bowing) suggestions and a lightly edited version that includes a minimal number of editorial markings.