Lip synchronization

In telecommunication, lip synchronization is the synchronization of audio and corresponding video signals so that there is no noticeable lack of simultaneity between them.

Note: An example of a lip synchronization problem is the case in which television video and audio signals are transported via different facilities (e.g., a geosynchronous satellite radio link and a landline) that have significantly differently delay times, respectively. In such cases it is necessary to delay the audio electronically to allow for the difference in propagation times.

Source: from Federal Standard 1037C and from MIL-STD-188