What is a "morpheme"?

A morpheme is a meaningful linguistic unit that cannot be divided into smaller meaningful parts without losing its meaning. It is the smallest unit of language that carries information and contributes to the overall meaning of a word. Therefore, the correct answer is C.

Options A and B are incorrect because they do not accurately describe what a morpheme is. Option A refers to a grammatical error, and option B refers to a sentence fragment, neither of which are related to the definition of a morpheme.

Option D is incorrect because a phoneme is a basic unit of sound in language and is not the same as a morpheme. Phonemes represent the different sounds that make up words, while morphemes represent the smallest units of meaning in language.