French Forces of the Interior
The French Forces of the Interior (FFI; French: Forces françaises de l'Intérieur) were French resistance fighters in the later stages of World War II. Charles de Gaulle used it as a formal name for the resistance fighters. The change in designation of these groups to FFI occurred as France's status changed from that of an occupied nation to one of a nation being liberated by the Allied armies.
Source: Wikipedia — French Forces of the Interior (CC BY-SA 4.0)