What is a Phoneme?

A phoneme is defined as the smallest unit of sound in a language that can distinguish one word from another. For example, the change in the initial sounds in the words "bat" and "cat" illustrates how phonemes can alter meaning; the /b/ and /k/ sounds at the beginning of these words represent different phonemes. This ability to create distinctions in meaning based solely on sound is crucial for effective communication and is a foundational element in the study of phonetics and phonology.

The other options refer to distinct linguistic concepts. A type of sentence structure relates to grammar and syntax, not to individual sounds. A unit of vocabulary pertains to words and their meanings, while a rule for word formation addresses how morphemes combine to create words. Each of these addresses aspects of language beyond the level of individual sounds that phonemes represent.