Flogging is a punishment: someone is hit again and again with a whip or a stick, hard, often on the back. Old armies, navies, and prisons used it; some places still do. It is cruel on purpose, meant to hurt and to control. The word is the -ing form of flog, so they flogged him and he was given a flogging are the same act. Though actually, in everyday British English flog has a second, much softer life: to flog something can mean to sell it, often fast or a bit pushy — He flogged his old bike. That selling sense is slang and has nothing to do with pain. When flogging stands alone as a noun, it almost always means the beating. It feels serious and old, not like a joke.