lip sync

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

• noun the synchronization of audio and video signals such that there is no lack of simultaneity between them
• verb to move the lips in synchronization with recorded sound

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

• noun combining audio and video recording in such a way that the sound is perfectly synchronized with the action that produced it; especially synchronizing the movements of a speaker's lips with the sound of his speech