The set of all possible output values of a function.
(The set of actual output values is called the range.)
In other words, the set of values that the output values lie in.
Example: the square of the natural numbers N = {1,2,3,...}:
• the domain (input values) is N
• the codomain (possible output values) is N
• the range (actual output values) is {0,1,2,4,9,16,...}
