A left curly brace delimiter used to denote sets, sequences, or function definitions in mathematics.
Examples
Set notation with explicit elements
A = \lbrace x, y, z \rbrace
Set builder notation
S = \lbrace x \in \mathbb{R} : x > 0 \rbrace
Function definition by cases
f(x) = \begin{cases} x^2 & \text{if } x \geq 0 \\ -x^2 & \text{if } x < 0 \end{cases}