Phoneme

The smallest unit of sound in a language that can distinguish one word from another. For example, the /b/ and /p/ sounds in "bat" and "pat" are different phonemes. American English has approximately 39 phonemes, compared to 26 letters in the alphabet. In accessibility and AAC contexts, phonemic interfaces allow users to select sounds rather than letters to compose messages, which can be more efficient because words typically require fewer phoneme selections than letter selections (14-20% fewer). Phonemic input also enables text-to-speech synthesis of any word or novel utterance, unlike word-based AAC systems that restrict users to predefined vocabularies.