The set of x-coordinates of the set of points on a graph; the set of x-coordinates of a given set of ordered pairs. The value that is the input in a function or relation.

The y-coordinates of the set of points on a graph. Also, the y-coordinates of a given set of ordered pairs. The range is the output in a function or a relation.

If you place a vertical line on a graph, you can tell whether it is a function. If the line intersects the graph at only one point, then the relationship is a function.