What's the difference between a relation and function

Relation-set of numbers w a relationship in domain and range
function- is a relation that has specific set of numbers that causes there to be only one range of numbers for each domain

A relation is a set of numbers that have a relationship through the use of a domain and range, while a function is a relation that has a specific set of numbers that causes there to be only be one range of numbers for each domain of numbers. All function are relations, but all are not functions. 
                                
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There are numbers that are related to each other in every relation. There could be a large variety range of numbers in the domain for a given range. For example, if x is equal to 23, then y could be equal to 46 or 11.5, depending on the factors that are being played into the domain.
 It can be concluded that if x equals 13, then y will always equal 26. There may be many numbers in a domain that lead to the same range in a function, but there will never be more numbers in a range than a domain. If the number of x changes to 14, then y will change to 28. Many mathematics use the term "well behaved" for the numbers that are part of the function.