What is a phoneme?

A phoneme is fundamentally understood as the smallest unit of sound in speech that can distinguish one word from another. This means that phonemes are crucial for our understanding of language, as they form the building blocks of spoken words. For example, changing the first phoneme in the word "bat" to "c" creates a different word, "cat," illustrating how phonemes can affect meaning.

The other options do not accurately represent what a phoneme is. For instance, the smallest unit of written language refers to letters or symbols found in writing and does not pertain to sound. A type of grammatical structure does not correlate to phonemes, as it involves the arrangement of words or phrases rather than individual sounds. Similarly, while sounds that change meaning in a word relate to phonemic differences, they do not describe phonemes in their entirety, as phonemes themselves are defined by their ability to distinguish rather than strictly by their role in meaning alteration.