Someone who fights a foreign occupation or domestic dictatorship by any means necessary including military. I'll give you an example.
Between 1933 and 1945, many thousands of people resisted the Nazis using both violent and non-violent means. Among the earliest opponents of Nazism in Germany were Communists, Socialists, and trade union leaders. Although mainstream church hierarchies supported the Nazi regime or acquiesced in its policies, individual German theologians such as Dietrich Bonhoeffer opposed the regime. Bonhoeffer was executed in 1945. Within the German conservative elite and the German military's General Staff small pockets of opposition to the Nazi regime existed. In July 1944, a coalition of these groups made an unsuccessful attempt to assassinate Adolf Hitler.
Resistance also occurred in Nazi-occupied areas outside Germany. In France, General Charles de Gaulle advocated open resistance against the collaborationist Vichy regime. After the German occupation of Denmark in April 1940, a resistance movement began operations there. Its activities included killing informers, raiding German military facilities, and sabotaging rail lines. In February 1941 the Dutch population mounted a general strike in protest against arrests and brutal treatment of Jews. In countries across Europe, underground resistance movements supplied forged documents to those in danger or arranged for safe hiding places or escape routes.
In the Soviet Union, Czechoslovakia, Yugoslavia, Greece, and Poland, guerrilla fighters, called partisans, offered armed resistance and engaged in anti-Nazi sabotage. In May 1942, Czech agents assassinated Reinhard Heydrich, the Nazi governor of the Protectorate of Bohemia and Moravia. In retaliation, the Nazis shot all of the men in the Czech village of Lidice. In August 1944, the Polish Home Army began a revolt (later known as the Warsaw Polish uprising). Within two months, the Nazis suppressed the rebellion. That same month, Slovak partisans launched an armed struggle (the Slovak national uprising) against the pro-German Hlinka government.
And another example.
When the war began, the British Colonists ("Americans") did not have a professional army or navy. Each colony provided for its own defenses through the use of local militia. Militiamen were lightly armed, slightly trained, and usually did not have uniforms. Their units served for only a few weeks or months at a time, were reluctant to go very far from home, and were thus generally unavailable for extended operations. Militia lacked the training and discipline of regular soldiers but were more numerous and could overwhelm regular troops as at the battles of Concord, Bennington and Saratoga, and the siege of Boston. Both sides used partisan warfare but the Americans were particularly effective at suppressing Loyalist activity when British regulars were not in the area.[4]
http://en.wikipedia.org/wiki/American_Revolutionary_War
Like in any war good or bad depends on your viewpoint. Some will say it was a good thing Americans resisted the British Empire, others might disagree and think a lot of the worlds misery could have been avoided if the UK had kept its colonies in check