What is a function?
A function is a rule which relates the values of one variable quantity to the values of another variable quantity, and does so in such a way that the value of the second variable quantity is uniquely determined by (i.e. is a function of) the value of the first variable quantity.
What is the relationship between x&y?
x the independent variable and y the dependent variable.
Is function a relation?
It is a relation as it has at least 2 variables with one of them depending on the other variable.