Guerrilla warfare is when people fight against a much larger and better-equipped army. Instead of meeting the army head-on, they use surprise and hit-and-run tactics like attacking enemies at night and then hiding quickly. They might also hide in forests, mountains, or other places that make it hard for the enemy to find them. Guerrilla warfare can last a long time because it's more about wearing down the enemy with small battles instead of winning one big battle.