Phonology is part of linguistics. Linguistics is the scientific study of language. Phonology is the science that studies the way that sounds (phones) carry meaning in language. Sounds (phones) that carry meaning in language are called phonemes. Sounds that do not carry meaning in the language are called allophones.
Phonology focuses on the study of phonemes, "units of sound (speech) that distinguish one word from another in a particular language." Phonology also includes studies of how words are articulated, or spoken.