OP_VAULT.

Proposed vaults: coins that must wait through a set delay before being spent, during which a backup key can pull them to safety.

If someone steals your keys, there is usually little you can do. With a vault, any withdrawal must wait, say a day, and during that wait the coins can be sent to a recovery path guarded by a much safer key. It needed new Taproot script instructions added by soft fork. BIP 443 was later proposed to replace it.