Slashing
The destruction of a portion of a validator's staked tokens as punishment for provably malicious behaviour.
Slashing is a penalty mechanism in Proof of Stake networks. When a validator commits a provably dishonest act — such as double-voting (signing two conflicting blocks at the same height) — a portion of their staked funds is automatically destroyed ('burned') by the protocol.
On Ethereum, slashable offences result in an initial penalty, forced ejection from the validator set, and a further 'correlation penalty' that increases if many validators are slashed simultaneously (implying a coordinated attack).
Slashing replaces the external energy cost of Proof of Work as the economic deterrent against malicious behaviour. It makes attacks costly for the attacker while not harming honest validators.