Additive identity
an element which, when added to any element x in the set, yields x
An additive identity is a special number inside of a set of numbers. In order for a number to be an additive identity, it has to be able to add to any other number in the set and equal that number. In math terms, that would be written as "n+x=n", where x is the additive identity, and n is any other number in the set.
The best-known example of an additive identity is the number zero.