Definition:Replacement Operation

Definition
The replacement operation on two variables $a$ and $b$ is denoted:
 * $a \gets b$

and is interpreted as:
 * the value of variable $a$ is to be replaced by the current value of variable $b$, while leaving the value of variable $b$ the same.

Also known as
The operation of replacement is also known as assignment or substitution.

Also see
Do not confuse with the left operation, which has the same notation but is interpreted in exactly the opposite manner.