Compound Paths

The Compound Paths command enables us to create paths that have transparent interior spaces where the original objects overlapped (such as the interiors of the letters o and g). This method lets us create objects more complex than we could easily create using the Drawing tools or Pathfinder commands.
Compound paths act as grouped objects. To select part of a compound path, we must use the Direct-selection tool.
Once we define objects as a compound path, all objects in the compound path take on the paint attributes of the backmost object in the stacking order. Releasing the compound path does not reapply the objects' previous paint attributes.
To apply Compound paths to objects
Select object > Compound Path > Make or Ctrl + 8 (Windows) or Command + 8 (Mac OS). To remove the effect
Select object > Compound Path > Release or Ctrl + Alt + 8 (Windows) or Command + Option + 8 (Mac OS).