Which term refers to a person's knowledge of what words mean, how they sound, and how they are used in a sentence?

The term that best describes a person's knowledge of what words mean, how they sound, and how they are used in a sentence is "lexicon." The lexicon encompasses the complete set of words and their meanings that a person understands and uses; it acts like a mental dictionary that includes not only the definitions of words but also their pronunciations and the rules for their appropriate usage in context.

In contrast, syntax refers specifically to the arrangement of words to form sentences, focusing mainly on structure rather than on the meanings of individual words. Phonetics is the study of the sounds of human speech but does not encompass the meaning or usage of words. Semantics deals with meaning in language, addressing how words, phrases, and sentences convey meaning, but it does not cover the complete spectrum of knowledge about words that the lexicon does. Thus, the lexicon is the most holistic term reflecting an individual's comprehensive understanding of language.