What does the term "phonetics" refer to?

The term "phonetics" specifically refers to the study of the sounds of human speech. This field encompasses the physical properties of sounds, how they are produced (articulatory phonetics), how they travel and are perceived (acoustic phonetics), and how they are interpreted by the brain (auditory phonetics). Phonetics provides essential insights into speech sounds that form the foundation for understanding language and communication.

Other options address different linguistic aspects but do not pertain to the core definition of phonetics. The study of sentence structure is related to syntax, the method of teaching vocabulary focuses on lexicon acquisition, and the study of written language pertains more to orthography and literacy than to the actual sounds of speech. Thus, recognizing that phonetics is specifically about sound makes the selection of this answer valid.