Sometimes a scatter plot shows an association that is not linear:

In this scatter plot, the data initially shows a negative trend then later a positive trend. Because the variables appear to be associated, but not in a linear way, we call this a non-linear association. In later grades, you will study functions that can be models for non-linear associations.

Sometimes in a scatter plot we can see separate groups of points.

A scatterplot with two groups of points.  The first begins near the origin and trends up and to the right toward 8 comma 13. Second group begins near 3 comma 25 and trends up and right toward 9 comma 45.

A scatterplot with two groups of points.  The first begins near the origin and trends up and to the right toward 8 comma 13. Second group begins near 3 comma 25 and trends up and right toward 9 comma 45. Each group is circled. 

We call these groups “clusters.” Clusters often appear when multiple patterns are present within the data. There may be subgroups within the overall data set that affect the variables.