A MappinG is simply a “rule” that assigns to each member of a Set A, a unique element of a set B. 
A MappinG is simply a "rule" that assigns to each member of a SeT A, a unique element of a SeT B. 
There are nonmathematical MappinGs?. Consider the “rule,” WGT that assigns to every living human being in United States their weight in pounds. Then the set A = {people living in the United States} and B = {x: 0<x<=1000}. For example: 
There are nonmathematical MappinGs. Consider the “rule,” WGT that assigns to every living human being in United States their weight in pounds. Then the set A = {people living in the United States} and B = {x: 0<x<=1000}. For example: 
There are mathematical MappinGs? as well. Consider the “rule,” ABS that assigns to each integer, its absolute value. Let set C = I, and the set D = I, also. Then, for example: 
There are mathematical MappinGs as well. Consider the “rule,” ABS that assigns to each integer, its absolute value. Let set C = I, and the set D = I, also. Then, for example: 
There are 4 basic kinds of MappinGs?. 
There are 4 basic kinds of MappinGs. 

In terms of formal SetTheory, a Mapping from X to Y is usually defined as a MathematicalRelation where each x in X is related to one, and only one, element of Y. This element is the image of x. However, there are lots of other equivalent definitions. 