Activism is working or campaigning for political or social change. Your activism as a college student might help you get a job with a human rights organization after you graduate.
There are many different kinds of activism — advocating for environmental regulations is one type of activism, and marching in the streets to protest the closing of your town's library is another kind. Any controversial social issues you can think of involve activism on both sides. This sense of the word has been around since 1920, from activist. The Latin root of both words is actus, "a doing, a driving."