A function is a specific type of relation. Both a function and a relation have input and output. A function is limited to only one output for each input, though. A relation has no limit on how many outputs each input can have.

Very good question. The different between relation and function is a relation is simply that : any x-value to create y-value while a function, however cannot be defined for multiple values of x

Good question. A relation is simply that; any x-value to create any y-value. A function, however, cannot be defined for multiple values of x. In other words, for a relation to be a function, it must have singular values for all x within its domain.

consumption is that money who you consume on any thing and the consumption function is that relation who tell you the consuming level on your every money income level.

A function is a special type of relation. So first let's see what a relation is. A relation is a diagram, equation, or list that defines a specific relationship between groups of elements. Now a function is a relation whose every input corresponds with a single output.