zmjezhd: Despite appearances, this is not a facetious reply: What a choral director does is conduct. The information conveyed by hand gestures (and by facial expression, though that is not so obvious to the audience) covers a lot of territory. In the first place, the tempo of the piece or, section of the piece, if the tempo varies, is established. Unlike an orchestral conductor a c.d. may not continue to mark the tempo through the piece except as need, choosing instead to indicate staccato or legato (notes separated or flowing together), loud or soft passages, accented notes, technical reminders of singing style, cues for entrances, cutoffs, sustained notes, accented notes, growing or diminishing volume, reminders to think a pitch a bit high so that it will not be sung flat (low). If necessary, the c.d. may choose to use Kodály Method hand signs to indicate specific relative pitches, although by concert time that should not be necessary. In a concert, much of what the c.d. does is to make adjustments: basses should sing a bit louder, sopranos should be careful of the vowel pronunciation on a particularly high note, altos need to show a bit more energy.
In most cases gestures do not have to be explained to the singers. They are a form of mime, mostly self-explanatory, a visual manifestation of the sound. Choral conducting seems to be an individual sport: each director has a style. If there is a systematized list of standard gestures (other than the Kodály) with a particular designation I have not run across it. I'll ask my choral director.
BranShea: In my experience the styles of orchestral and choral conducting are quite different, even when done by one individual, and even when conducting both in the same piece. We recently performed Beethoven's Ninth Symphony, and it was always easy to tell from the gestures whether the conductor was focused on the choir or the orchestra at any given moment. But yes, the overall purpose is essentially the same.
