the doctrine or practice of vigorous action or involvement as a means of achieving political or other goals, sometimes by demonstrations, protests, etc.
2.
Philosophy.
a.
a theory that the essence of reality is pure activity, especially spiritual activity, or process.
b.
a theory that the relationship between the mind and the objects of perception depends upon the action of the mind.
Origin: 1905–10; < German Aktivismus.See active, -ism