SATB
In music, SATB is an initialism for soprano, alto, tenor and bass, defining the voice types required by a chorus or choir to perform a particular musical work. Pieces written for SATB (the most common combination, and used by most hymn tunes) can be sung by choruses of mixed genders, by choirs of men and boys, or by four soloists.
There is a lack of general agreement on other initialisms and abbreviations. Tr for treble, Mz (or similar) for mezzo-soprano, Ba, Bar or Bari for baritone are self-explanatory, while C could be taken for canto, the highest part, or for contralto, usually implying a female alto(s) as opposed to a countertenor (Ct).
SATB div. (divisi, or divided) denotes that one or more individual parts divide into two or more parts at some point in the piece, often sharing the same staff. A single choir with two of each voice type should be written SSAATTBB, unless it is laid out for two identical choirs, in which case it is SATB/SATB. Publishers usually include such descriptions in their catalogues of choral works, although many fail to provide sufficient detail, commonly omitting, for example, the term div. where it is required fully to describe the resources required by the composer. Also misleading can be the use of B for a baritone part or S for an Mz part as for example in Stanford's motet "Eternal Father" which, though marked SSATBB, is for one each of soprano, mezzo-soprano, alto, tenor, baritone and bass.
Instrumental music
SATB can to also refer to ensembles of four instruments from the same family, such as saxophones (soprano, alto, tenor and baritone) or recorders. Individual contrapuntal parts of many instrumental compositions, particularly fugues, such as those found in Bach's "The Art of Fugue" and "The Musical Offering", may also be called SATB without implying any correlation with vocal ranges.