In mathematics, a "map" is another word for a function.
It describes a rule that takes an input and gives you a specific output.
Example: to double each number in a list, a "map" is the rule that says "multiply by 2", so if we put in the number 3, the map sends it to 6 (because 3 x 2 = 6).
Note: in general language a map is a diagram of a place.