In phonetics and linguistics, the phonetic environment of a given instance of a speech sound (or "phone") consists of the other phones adjacent to and surrounding it. The phonetic environment of a phone can sometimes determine the allophonic or phonemic qualities of a sound in a given language.
For example, the English vowel 'a' /æ/ in the word 'mat' /mæt/ has the consonants /m/ preceding it and /t/ following it. In linguistic notation it is written as /m_t, where the slash can be read as "in the environment", and the underscore represents the target phone's position relative to its neighbours.[1] The expression therefore can be read as "in the environment after m and before t".