How to tell if something is a function or a relation:
A relation is any set of ordered pairs. These pairs consist of inputs and outputs, (x, y). Relations describe how one set (the domain) is associated with another set (the range).
Example of a Relation:
{(1,2),(2,3),(3,4),(2,5)} See how the #2 is paired with #3 and #5. This is an example of how the #2 is a relation as it has more than one partner.
A function is a special type of relation with a specific rule: each input is related to exactly one output: no input value is paired with more than one output value.
Example of a Function:
{(1,2),(2,3),(3,4)} Each input 1, 2 and 3 is paired with exactly one output.