lip synch (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.
lip synch (Verb) — Move the lips in synchronization (with recorded speech or song). ex. "The best rock 'n' roll TV performers look at lip-synch shows as an opportunity to perform in ways that the mechanics of live don't allow"