12 is the first abundant number.
12 is the second semiperfect number.
12 is a friendly number.
A set of 12 objects is often called a dozen. That type of set gets its own name because many things are grouped in twelve: for example, twelve months in a year, twelve inches in a foot, twelve eggs in a typical container, etc.
There are 12 size-3 Latin squares.
In Greek-based number-naming systems, 12 is associated with prefix "dodeka-", and with prefix "duodeci-" in Latin systems.
In the Czech and Slovak languages, 12 is called tucet.