Vote snapshot (checkpoint)

The term has two meanings worth separating. The technical one is the on-chain checkpoint: a history of voting balances that lets you query an account's power "at block X." In OpenZeppelin's ERC20Votes and in Compound or GovernorBravo, every transfer or delegation writes a checkpoint pairing a block with a voting balance. When a proposal is created, a reference block is fixed and each account's power is read with functions like getPriorVotes or getPastVotes against that historical block. The EIP-6372 standard defines which clock a contract uses, block number or timestamp. The other meaning is Snapshot.org, a gasless off-chain voting platform: it shares the "snapshot at a block" idea but is not the same thing.

It closes the door to time-based manipulation of the vote. If power is measured at a fixed past block, borrowing a million tokens right before voting is useless, because at the reference block the attacker did not hold them. The absence of this safeguard was the root cause of the 2022 Beanstalk incident.