Audio post production is the general term for all stages of production happening between the actual recording in a studio and the completion of a master recording. It involves sound design, sound editing, audio mixing, and the addition of effects.
Film: Audio post production usually refers to the post-production of audio that is synchronized with video. This applies to TV, cinema, and commercials.
Music: The post process in recording acoustic music is often referred to as mixing, as this process happens after recording the musicians. In electronic music the workflow is usually quite different, and in this context the term "post processing" would typically not refer to the actual mixing process but rather what is applied to the resulting mix-down.