A resistance movement is a group or collection of individual groups, dedicated to fighting an invader in an occupied country or the government of a sovereign nation through either the use of physical force, or nonviolence. The term resistance has political overtones, as people have used it, along with similar terms, to bring support to opposition groups.
Organizations and individuals critical of foreign intervention and supporting forms of organized movement (particularly where citizens are affected) tend to favor the term. When such a resistance movement uses violence, those favorably disposed to it may also speak of freedom fighters. Both phrases -- resistance movement and freedom fighters -- can become contentious terms for what other observers might describe as terrorists, though this is controversial as terrorists are often criticised and seen as morally wrong, whereas many see Resistance Movements as legitimate. The popular saying "One person's terrorist is another person's freedom fighter" encapsulates this dichotomy, without clarifying the distinction that freedom fighters must, by definition, be fighting for freedom. Terrorists, as a modern appellation, are not seen as fighting for freedom, whereas Resistance Movements are. Thus, Resistance Movements may employ terror tactics, but not all who use terror tactics are correctly called a Resistance movement.

Background
According to Joint Publication 1-02, The United States Department of Defense defines a resistance movement as: An organized effort by some portion of the civil population of a country to resist the legally established government or an occupying power and to disrupt civil order and stability.
In strict military terminology, a resistance movement is simply that; it seeks to resist (change) the policies of a government or occupying power. This may be accomplished though violent or non-violent means. It must be noted that a resistance movement is specifically limited to changing the nature of current power, not to overthrow it. The correct military term for removing or overthrowing a government is an insurgency.

US government definition

Examples of resistance movements

Algerian resistance
Armenian resistance
Basque separatists (ongoing)
Black Panther Party
Bosnian Resistance
Chechen separatists (ongoing)
Colombian communist resistance (ongoing)
Cuban anti-Batista resistance
Cuban anti-Castro resistance (ongoing)
Czechoslovakian resistance
Greek resistance
Environmentalist resistance (ongoing)
Hungarian Uprising
Human rights resistance (ongoing)
Indian Independence movement
Iraqi insurgency (ongoing)
Irish Republicanism in particular (ongoing)
Jewish Zionist resistance to British occupation in Mandate Palestine
Khalistan (ongoing)
Kurdish separatism (ongoing)
Lebanese Islamic Resistance (ongoing)
Militant Islam (ongoing)
National Front for the Liberation of South Vietnam
New Black panthers (ongoing)
Polish resistance
Palestinian Resistance (ongoing)
Romanian anti-communist resistance movement
Somali Popular Resistance Movement in the Land of the Two Migrations (ongoing)
Tamil Tigers (ongoing)
Tibetan resistance movement
Tupamaros
Sandinistas
South Thailand insurgency (ongoing)
Sudanese resistance (ongoing)
Viet Minh
West Sahara Independence Intifada (ongoing)
Ulster Loyalism (ongoing)
Zapatistas (ongoing) post-World War II
See also Resistance during World War II
Planned resistance movements:

Albanian resistance movement
Austrian resistance movement (O5)
Belgian resistance movement
Bulgarian resistance movement
Burmese resistance movement
Czech Resistance movement
Chinese resistance movements

• Northeast Anti-Japanese United Army
  Anti-Japanese Army For The Salvation Of The Country
  Chinese People's National Salvation Army
  Heilungkiang National Salvation Army
  Jilin Self-Defence Army
  Northeast Anti-Japanese National Salvation Army
  Northeast Anti-Japanese United Army
  Northeast People's Anti-Japanese Volunteer Army
  Northeastern Loyal and Brave Army
  Northeastern People's Revolutionary Army
  Northeastern Volunteer Righteous & Brave Fighters
  Hong Kong resistance movements
  Gangjiu dadui (Hong Kong-Kowloon big army)
  Dongjiang Guerillas (East River Guerillas, Southern China and Hong Kong organisation)
  Danish resistance movement
  Dutch resistance movement
  Estonian resistance movement
  French resistance movement in World War II, including the
  
  
  
  • Maquis
    German resistance movements
    
    
    
    • The White Rose
      The Red Orchestra
      Greek resistance movement
      Italian resistance movement
      Jewish resistance movement, including Jewish partisans and Jewish Anti-Fascist Committee
      Latvian resistance movement
      Lithuanian resistance during World War II
      Lithuanian, Latvian, and Estonian ("Forest brothers") resistance movements during the Soviet invasion and occupation of the Baltic countries (continued after the end of WWII).
      Norwegian resistance movement
      Philippine resistance movement -- the anti-Japanese phase of the Huk movement
      Polish Secret State and resistance organizations:
      
      
      
      • Armia Krajowa (the Home Army), Polish underground army in World War II (400 000 sworn members)
        Narodowe Siły Zbrojne
        Bataliony Chłopskie
        Gwardia Ludowa (the Peoples' Guard) and Armia Ludowa (the Peoples' Army)
        Żydowska Organizacja Bojowa (ZOB, the Jewish Fighting Organisation), Jewish resistance movement that led the Warsaw Ghetto Uprising in 1943
        Zydowski Zwiazek Walki (ZZW, the Jewish Fighting Union), Jewish resistance movement that led the Warsaw Ghetto Uprising in 1943
        Slovak resistance movement
        Soviet resistance movement of Soviet partisans and underground which had Moscow-organized and spontaneously formed cells opposing German occupation.
        Thai resistance movement
        Ukrainian Insurgent Army - fought the Poles, the Germans and the Soviets.
        Yugoslav resistance movements:
        
        
        
        • People's Liberation Army – the partisans
          Yugoslav Royal Army in the Fatherland – Chetniks
          The Auxiliary Units, organized by Colonel Colin Gubbins as a potential British resistance movement against a possible invasion of the British Isles by Nazi forces, note that it was the only resistance movement established prior to invasion, albeit the invasion never came. World War II
          
          Irish Republican Army
          The Rising of East Karelians (1921-1922)
          Lwów Eaglets
          Non-Cooperation Movement (1919-1939)
          Filipino guerilla units after official end of Philippine-American War (1902-1913)
          Pancho Villa led a resistance movement/rebellion in Mexico in the early 20th century, as did the Zapata brothers.
          Bolshevik Revolution (1917-1922) Pre-World War II
          
          Carbonari - 19th century Italian movement resisting Austrian or Bourbon rule.
          Sons of Liberty - Revolutionary patriot group that embraced Republicanism in the United States during the 1760's and 1770's and routinely engaged in acts of violent resistance against British government officials and prominent loyalist sympathizers. The Boston branch of the Sons of Liberty met under the Liberty Tree, from which they would post messages or hang and burn effigies of their enemies.
          The Underground Railroad - The pre American Civil War slave escape network consisting of volunteers who were dedicated to secretly helping escaping slave reach free states or Canada. Pre-20th century