Expulsion means forcing someone to leave a place or group, usually as a serious punishment. When a student gets expelled from school, they're removed and told they can no longer attend that school. Schools typically reserve expulsion for the most serious rule violations, like bringing weapons, repeated violence, or dangerous behavior that threatens other students.

Expulsion isn't a polite request to leave: it's being pushed out with no option to return. A country might order the expulsion of a foreign diplomat who's broken international law. A club might vote for the expulsion of a member who's violated their rules.

The verb form is expel. When something is expelled, it's thrust out forcefully. Your lungs expel air when you exhale. A volcano expels lava and ash. In these cases, the word emphasizes the outward force involved.

Because expulsion is such a severe consequence, most organizations treat it as a last resort, used only when someone has shown they can't follow the fundamental rules that keep everyone safe or make the group function.