An extra-parliamentary opposition is a political movement opposed to a ruling government or political party that chooses not to engage in elections. Many social movements could be categorized as an extra-parliamentary opposition.
Extra-parliamentary opposition Wikipedia
The German New Left movement Außerparlamentarische Opposition (APO, Extraparliamentary Opposition) is one of the best known examples of this phenomenon. The APO challenged the grand coalition of the Social Democratic Party and the Christian Democratic Union, which controlled 95 percent of the seats in the Bundestag between 1966 and 1969.
The Italian Far Left movement Lotta Continua (LC - Continuous Struggle) is one of the best known examples of this phenomenon in Italy.