noun /ˈdɑɪ.ə.ˌlɛkt/
a) A variety of a language (specifically, often a spoken variety) that is characteristic of a particular area, community or group, often with relatively minor differences in vocabulary, style, spelling and pronunciation.
A language is a dialect with an army and a navy.
b) A dialect of a language perceived as substandard and wrong.
Many even deny it and say something like this: "No, we dont speak a dialect around here.
Wikipedia foundation.