What best defines a morpheme in linguistics?

A morpheme is defined as the smallest meaningful unit of language. This means that a morpheme can stand alone as a word, like "book" or "cat," or it can be a prefix or suffix that adds meaning to a word, such as "un-" in "unknown" or "-ing" in "running." Each morpheme conveys specific information, which is crucial for understanding the structure and meaning of language. Recognizing that morphemes can be both free (able to stand alone) and bound (attached to other morphemes) is essential for grasping how they function in linguistic constructions.

The other options do not accurately capture the essence of a morpheme. Basic sound units pertain to phonemes, not morphemes, which are about meaning. Grammatical structures involve more complex arrangements of words and phrases, whereas morphemes are the fundamental building blocks. Finally, a representation of phonetic sounds relates more to phonetics and phonology, rather than to the meaningful units that morphemes embody within a language.