Definition
To sweep a private key is to broadcast a transaction that sends the entire balance from an address controlled by that key into a fresh address inside your own wallet. After a sweep, the original key holds zero satoshis, so any lingering copy of it, on a paper wallet, a backup, or a compromised device, is harmless. Sweeping is the recommended way to claim funds from paper wallets, gift cards, and any key whose history of exposure you cannot fully account for.
Sweep versus import
Importing a private key merely adds it to your wallet's keychain; the coins stay at the original address and are still spendable by anyone holding a duplicate of that key. Sweeping moves the value to a key that only your wallet knows. The rule of thumb for paper wallets and untrusted keys is always sweep, never import, because importing preserves the security risk that the original key was copied or photographed.
Privacy considerations
A naive sweep that combines several swept UTXOs with your existing coins can link them together under the common-input-ownership heuristic, undoing wallet separation you may have wanted to keep. Privacy-conscious users sweep into a fresh, isolated account or use coin-control labeling afterward. Sweeping is also the standard recovery action after a seed phrase or key may have been exposed: move first, investigate later.
For the surveillance assumption a careless sweep can trip, see our Common-Input-Ownership Heuristic entry, and review Address Reuse for why fresh destinations matter.
In Simple Terms
To sweep a private key is to broadcast a transaction that sends the entire balance from an address controlled by that key into a fresh…