The definition of activism is the use of direct action to achieve an end, either for or against an issue.
When people tie themselves to trees to protect the forest from being cut down, it is an example of activism.
the doctrine or policy of taking positive, direct action to achieve an end, esp. a political or social end
The use of direct, often confrontational action, such as a demonstration or strike, in opposition to or support of a cause.
active + -ism