Equal

Two quantities are said to be equal if they are, in some well-defined sense, equivalent. Equality of quantities $a$ and $b$ is written $a=b$.

A symbol with three horizontal line segments ($\equiv$) resembling the equals sign is used to denote both equality by definition (e.g., $A\equiv B$ means $A$ is Defined to be equal to $B$) and Congruence (e.g., $13\equiv 1\ \left({{\rm mod\ } {12}}\right)$ means 13 divided by 12 leaves a Remainder of 1--a fact known to all readers of analog clocks).

See also Congruence, Defined, Different, Equal by Definition, Equality, Equivalent, Isomorphism