An example function table can be represented by two horizontal rows, one which contains known data and the other that is variable upon the first. The first row is called input and the second is output. The output is based on the "rule" applied to the input.
Each function defines a rule or set of rules that is applied to an input, denoted as "x" on a function table. After the rules are applied, the output is the answer, denoted as "y" on a function table. For instance, if the inputs, or x values, are four, six and nine, and the rule is multiply by two, then the corresponding outputs, or y values, are eight, 12 and 18.