Linguistics is the science of language, or the academic study of language.
As language is to communication, so linguistics is to semiotics. Linguistics is a branch of semiotics, in other words. This formal hierarchy overlooks or, at least, obscures the problem of language use for purposes other than communication, such as phatic communion, a term coined by the anthropologist Bronislaw Malinowski. Most linguists study only the natural language of human beings, so Linguistics could easily be considered a branch of anthropology.