What is the secret organization in a country to oppose the forces in occupation?

The secret organization opposing occupying forces in a country is often referred to as a resistance movement or insurgency. These groups typically engage in covert operations, sabotage, and guerrilla tactics to undermine the authority and control of the occupying power. They may operate independently or be part of a larger coalition of factions united by a common goal of liberation and self-determination. Examples include the French Resistance during World War II and various groups in contemporary conflicts.