What is "rump state"

n. Any politico-geographic entity (a state) that is the remnant of a previous, larger one that has been broken up

A rump state is the remnant of a once-larger state, left with a reduced territory in the wake of secession, annexation, irredentism, occupation, decolonization, or a successful coup d’état or revolution on part of its former territory. In the latter case, a government stops short of going into exile because it still controls part of its former territory. For example, after the Qing government assumed control over most of China, the previous Ming regime turned to resistance in the south until its eventual conquest.