A snapshot is a record of the blockchain's state at a specific block number. It shows exactly who owned which tokens at that precise moment. By doing this, voting rights are based on actual holdings fixed at the time of a proposal. Without a snapshot, a user could vote, transfer their tokens to another account they control, and vote again, effectively double spending their voting power. This process of locking the data at a single point in time to prevent such abuse is what gives Snapshot its name.