Viseme

The visual equivalent of a phoneme — the distinct mouth shape or lip position that corresponds to a speech sound as seen on a speaker's face. Unlike phonemes, which are auditory units, visemes are visual units that represent how the mouth looks during speech production. Multiple phonemes may map to the same viseme (for example, the sounds /p/, /b/, and /m/ all produce similar lip positions), which is one reason lip-reading is challenging. Visemes are important in accessibility contexts for lip-reading support tools, sign language animation, and visual speech synthesis systems.