A relation is simply a set of ordered pairs, while a function is a set of ordered pairs in which each x-coordinate has only ONE y-coordinate associated with it.
The first elements in the ordered pairs (the x-values), form the domain. The second elements in the ordered pairs (the y-values), form the range.
In the set,
{(1, 3), (2, 3), (3, 3), (4, 3)}
it is not a function, based on the definition since an x-coordinate has the same y-coordinate which is 3.
