Active skill
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From Diablo Wiki
Active skills are in opposition to passive skills. Active skills must be cast or used directly with the mouse button or one of the hotkeys. These are skills you use while fighting monsters, often in place of the basic attack function.
Many active skills are boosted by passive skills. Some active skills have synergistic properties, and receive or grant bonuses to other skills.
Only active skills are considered signature skills for classes.
Only active skills have sockets for Skill Runes.