1. Originally, the science of vocal sounds (phonetics); especially, of the sounds of a particular language. The study of pronunciation, transferring the system of sounds in a language. Now, that branch of linguistics that deals with sound systems, or with sound systems and phonetics; the study of the sound system of a particular language. The ensemble for a particular individual speaker is referred to as his/her phonological system.
2. The analysis and description of speech sounds in terms of the linguistic systems in which they function.
3. The study of the elements and principles that determine the overall sound patterns of a language, including phonetics and phonemics.