The graph to the right shows a **positive linear** relationship between two variables, **P** and **Q**. Values of **P** are shown on the vertical axis, and values of **Q** are shown on the horizontal axis. The relationship shown is called a **positive** relationship because larger values of **P** are associated with larger values of **Q**. Where **P = 4** we can see that **Q = 6** and when **P = 10** we see that **Q = 15**. The relationship is termed **linear** because its graph is a straight line.

This particular graph is a graph of a supply curve,^{3} which is why it is labeled **S**. It shows the relationship between market price, **P**, and quantity supplied, **Q**.

^{3} Don't worry about understanding Supply curves at this point. For now, just be sure you understand the meaning of a positive linear relationship. Even though it's a straight line we call it a "curve" to remind us that sometimes Supply is not graphed with a straight line.