\Coloneq
The symbol \Coloneq is used to denote a definition or assignment, where the left-hand side is defined to be equal to the right-hand side. It is often used in mathematical texts to clarify that a particular expression is being defined as something else.
Defines x as the sum of a and b.
x \Coloneq a + b
Defines the function f(t) as a quadratic expression.
f(t) \Coloneq t^2 + 3t + 2
Defines the set A as the set of all positive real numbers.
A \Coloneq \{ x \in \mathbb{R} \mid x > 0 \}