Post-production occurs in the making of audio recordings, films/movies, videos and television programs. It is the general term for all stages of production happening between the actual recording and the complete record, film or video.
Post-production is in fact many different processes grouped under one name. These typically include:
Editing the picture.
Editing the soundtrack.
Writing and recording the soundtrack music.
Adding visual special effects - mainly computer generated imagery and digital compositing.
Adding audio sound effects - like ADR, Foley, sound design and sound designers' actions.
Color grading, and negative cutting the final master copy from which release prints will be made (although this may be made obsolete soon by digital cinema technologies).
Typically, the post-production phase of creating a film takes longer than the actual shooting of the film, and can take several months to complete.