Vernacular, the noun, is the native language of a place. It can also refer to the everyday expressions used by people or to the vocabulary used inside a particular place or profession. The adjective means native or indigenous.
“Super Freakonomics” also tiptoes around important public policy debates such as healthcare and doesn’t dare venture into any sort of policy prescriptions using the political vernacular of the day. (LA Times)
The son of a farm labourer, Clare also wrote poetry on unrequited love, the sometimes fragile nature of his mental health – he was twice admitted to asylums – and described the natural world in his local vernacular rather than the standard English deployed by his Romantic peers. (The Guardian)