Activism, in a general sense, can be described as involvement in action to bring about change, be it social, political, environmental, or other change. This action is in support of or opposition to one side of a controversial argument.
There are many different forms of activism; a select list follows.
... a Christian and possibly bishop of Croton. In approximately 580, he wrote "De origine actibusque Getarum[?]" (The origin and deeds of the Goths), "De breviatione ...