A relational symbol indicating equality with a dot above, commonly used to define quantities or show natural isomorphisms.
Examples
Definition of a sequence term
a_n \doteq \frac{n^2 + 1}{n^2} \text{ for } n \geq 1
Definition of a function
f(x) \doteq x^2 + 2x + 1
Definition equality in abstract algebra
G/H \doteq \{gH : g \in G\}