In phonetics and linguistics the phonetic environment refers to the surrounding sounds of a target speech sound, or target phone, in a word. 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] in the word 'mat' [mat] 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. The expression therefore reads "in the environment after m and before t".