Active skills window
From Diablo Wiki
The active skills window is a pop up window that's part of the game interface. It appears just above the belt interface, and displays all of a character's available active skills. This means only the skills that can be mapped to the mouse buttons or the 1234 keys. This does not include passive skills, or skills that don't have any points in them or are otherwise unusable.
See the Interface page for much more.
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