Slashing is the loss of committed stake imposed under a protocol's rules for particular violations. Its purpose is to make behavior that threatens security economically costly. It can affect a validator's own funds and, depending on the system, assets delegated or pooled with that validator.
What can trigger a slash
Ethereum can slash validators for signing conflicting block proposals or incompatible attestations. Such violations can result from faulty operations, including running the same signing keys in conflicting setups, without requiring malicious intent. A slashed Ethereum validator is also forced to exit validation.
Ordinary missed duties or downtime can produce lost rewards and other penalties without constituting slashing. Other networks and restaking services define their own offenses and enforcement mechanisms, so Ethereum's conditions should not be assumed everywhere.
Who bears the loss
Penalty size depends on protocol rules and circumstances. On Ethereum, correlated slashing events can increase losses when more stake is slashed around the same time. There is no universal fixed percentage.
For pooled or delegated staking, the provider's accounting and loss-sharing rules determine the exposure passed to participants. Operator diversification and safeguards can reduce some risks, but neither delegation nor an advertised protection arrangement guarantees full reimbursement after a slash.