Lip syncing

Lip sync (short for lip synchronization) is a technical term for matching a speaking or singing person's lip movements with prerecorded sung or spoken vocals that listeners hear, either through the sound reinforcement system in a live performance or via television, computer or cinema speakers in other cases. The term can refer to any of a number of different techniques and processes, in the context of live performances and audiovisual recordings.

In film production, lip-synching is often part of the postproduction phase. Dubbing foreign-language films and making animated characters appear to speak both require elaborate lip-synching. Many video games make extensive use of lip-synced sound files to create an immersive environment in which on-screen characters appear to be speaking. In the music industry, lip-synching is used by singers for music videos, television and film appearances and some types of live performances. Lip-syncing by singers can be controversial to fans attending concert performances who expect to view a live performance.

Lip sync is also referred to as "lip-sync" or "lip-synch". The term "sync" or "synch" is pronounced the same as "sink".

Lip-synching is considered a part of miming. It can be used to make it appear as though actors have substantial singing ability (e.g., The Partridge Family television show), to simulate a vocal effect that can be achieved only in the recording studio, e.g. Cher's Believe, which used an Auto-Tune effects processing on her voice; to improve performance during choreographed live dance numbers that incorporate vocals; to misattribute vocals entirely (e.g., Milli Vanilli, a band which lip-synced to recordings made by other singers), or to cover deficiencies in live performance. It is also commonly used in drag shows. Sometimes lip sync performances are forced on performers by television producers to shorten the guest appearances of celebrities, as it requires less time for rehearsals and hugely simplifies the process of sound mixing, or to eliminate the risk of vocal errors. Some artists lip sync because they are not confident singing live and want to avoid singing out of tune.

...
Wikipedia