Secession: Secession refers specifically to when a region formally withdraws its membership from an existing political entity like a nation-state.
Autonomy: Autonomy is having self-governance or control over one's own affairs. In the context of separatist movements, it often refers to regions seeking greater political or administrative power within a country.
Irredentism: Irredentism is when a separatist movement seeks to join together a region with its ethnic or cultural kin in another country. It aims to reunite people who share a common heritage but are divided by national borders.