Private key

A private key is a secret number that controls the crypto tied to an address and is used to authorise (sign) transactions. Whoever holds it can move the funds, which is why it must never be shared or exposed. Public keys and addresses are derived from the private key, but the key itself cannot be reconstructed from them.

A common misconception is that coins are “stored” inside a wallet; the blockchain holds the balances, and the private key is simply what proves the right to spend them. See public and private keys explained for more.