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.
... Paul Anka
1981 Joni Mitchell
1982 Neil Young
1983 Glenn Gould
1986 Gordon Lightfoot
1987 The Guess Who[?]
1989 The Band
1990 Maureen Forrester[?]
1991 ...