DA - Digital audio (fadeable audio). This is the prefix on all regular audio.

AX - Prefix for satellite programs. This is not a timed event and can only be stopped with a hard sync, pin closure or manual intervention by jock
AT - Aux timed event, similar to the AX, but allows you to specify an expiration time.
ST and SD - satellite tone and satellite tone delay - Used to fire satellite liners.
VO - voice over, non fadeable - set the eom at the beginning of the element so it will play over another element.
VP - voice over protect -similar to VO but this protects the vocals of the next element from been played over.
AP - auxiliary pulse, used by the SS32 to send a closure(tone).