The document discusses relations and functions. A relation is a set of ordered pairs where the first elements comprise the domain and the second elements comprise the range. A function is a special type of relation where each domain element is paired with exactly one range element. The vertical line test can be used to determine if a relation is a function by seeing if a vertical line can intersect more than one point. Several examples of relations and functions are provided and it is asked whether the relations are functions using the vertical line test.