Layers are the surfaces that are displayed in the Map window. Different layers can store different types of information, and you can display, hide, and reorder layers according to your needs.
Layers are stored in separate collapsible lists on the Layers tab. There is one list for each layer group.
Everything in the Map window is contained in a particular layer. For example, any drawings that you create are stored in a single drawings layer. Similarly, any query results that you add to the Map window are stored in query results layers. There is one layer for each set of results.