Definable type
= Definable type
{wiki}
A type $p(x)$ over a model $M$ is definable when, for every formula $\varphi(x;y)$, there is an $M$-formula $d_p\varphi(y)$ such that
$$
\varphi(x;b)\in p
\quad\Longleftrightarrow\quad
M\models d_p\varphi(b)
$$
for every tuple $b$ from $M$.