This answer to this question about η-equivalence in Coq draws a distinction between judgmental equality and definitional equality.
In the simply typed lambda calculus (henceforth STLC), the following is an example of a typing rule.
$$ \frac{\Gamma \vdash t_1 : \alpha \to \beta \;\; \text{and} \;\; \Gamma \vdash t_2 : \alpha}{\Gamma \vdash t_1(t_2) : \beta } \;\; \text{is modus ponens} $$
In my understanding, $t_1 : \alpha \to \beta$ is a typing judgment.
STLC can be formalized using typing judgments exclusively.
Judgmental equality is slightly more confusing.
Does it refer to a new type of judgment such as $t_1 = t_2$ for terms and $\alpha_1 = \alpha_2$ for types, as described here?
I think an equality type is just a type $t_3 : \alpha \equiv \beta$ that can be inhabited or not like any other type.
Assuming the above is true, then, I'm not sure what definitional equality would be.