Private Key
The secret code that controls a crypto wallet. Whoever holds it owns the funds — lose it and they are gone.
A private key is the secret number that controls a crypto wallet. Signing a transaction with it proves ownership, so whoever knows the key is, for all practical purposes, the owner of the funds. Wallets usually back it up as a 12- or 24-word seed phrase.
Two rules follow. First: never share the key or seed phrase with anyone, type it into a website, or store it in cloud notes — the overwhelming majority of crypto theft is stolen keys, not broken blockchains. Second: if you lose it, no company can restore access; an estimated several million Bitcoin are permanently stranded this way. “Not your keys, not your coins” summarizes why many holders prefer self-custody over leaving assets on exchanges.