Here’s a great post explaining some terms used in the movie business for sound recording and the various stages of the process, along with an idea of the personnel involved in each position. Some of the terms are familiar such as ADR (Automatic Dialogue Replacement) or Foley (recording sound effects live to sync with the picture e.g. footsteps), others less so. My personal favorite is ‘Walla’ –
Additional audio is recorded for groups of people. This is usually for background sounds, like guests in a restaurant. The term “walla” comes from the fact that actors were (and often still are) instructed to say “walla, walla, walla” instead of real dialogue. The point is to create a sound effect of a crowd murmuring, without any recognizable dialogue line being heard. You don’t want anything distinctive to stand out above the murmur, other than the lead actors’ dialogue lines.