Answer:
It's a relation.
Explanation:
When a graph is given and we wanna know if it's a function or a relation, we have to use the vertical line test, which consist in drawing a vertical line across the figure, if the vertical line cuts the graph in two points, then it's just a relation, but if it cuts the graph in only one points, we can determined that it's a function.
In this case, the graph given belongs to a relation, it's not a function, because a vertical line would cut it in two points. Other example of relations are circumferences or hyperbolas.
(An image showing this test is attached).