In addition to the standard fixed legend (which identifies patterns and colors used to mark individual plots in the graph), there are also other more specialized types of fixed legends. For example, there are contour legends that identify the levels in surface or contour plots:
icon legends that identify the assignment of icon features to specific variables:
or selection legends that identify the case selection conditions used to classify cases into multiple subsets shown on the graph.
All these fixed legends can be changed to movable legends following the same conventions outlined in Can I Customize the Location and Format of the Legend?.