sound effect

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An imitative sound, as of thunder or an explosion, produced artificially for theatrical purposes, as for a film, play, or radio program.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An artificially created or enhanced sound, used to accompany the action of a dramatic production, such as a film, play or video game

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an effect that imitates a sound called for in the script of a play