A function table displays the relationship between the inputs and outputs of a specified function. A function table will also follow the rules of a function in that every input only produces one output.

Inputs are more popularly called the domain of a function. It is used very often in math to restrict the domain to only the real numbers or to only the integers.

Outputs are more popularly called the range or image of a function. While the domain can be easily restricted, it is much harder to do so with the image because it has more flexibility.

An example of a function is one where it takes a number and doubles it. For example, one input is 7 while the corresponding output is 14. Many more complex functions exist, even involving imaginary numbers.