A cold wallet is a way to store cryptocurrency keys offline. The wallet may be a hardware device, a carefully stored paper backup, or another setup where the private key is not kept on an internet-connected phone or computer.
Why cold wallets are used
Cold storage is useful for long-term holdings because attackers cannot steal the key through a normal website login or exchange account breach. The tradeoff is convenience: moving funds usually takes more effort than using a hot wallet.
What can go wrong
A cold wallet is not magic protection. If the seed phrase is photographed, stored in cloud notes, typed into a fake wallet app, or lost entirely, the funds can still be stolen or become unreachable.
For many crypto users, a cold wallet is best for savings while a smaller hot wallet handles everyday transactions.