A graph or chart is a line or a diagram that visually depicts the relationship between two quantities. Graphs allow you to depict large amounts of information in a concise, visual format.
If you're a student, there are two main applications of graphs that you'll see in school. The first is to represent a collection of data. Several types of graphs, such as line charts, pie charts, bar graphs, and others, are used for this purpose. The second is to graphically represent a function. In this case, the function is graphed in a manner similar to a line chart, with the function taking the form of a curve on the Cartesian plane.
Sources used (see bibliography page for titles corresponding to numbers): 60.