Glossary
What is a private key?
In one sentence
A private key is the secret number that lets you spend the crypto at a given address. Whoever holds it controls the funds.
A private key is an enormous random number. From it, mathematics derives a public key and an address that you can share freely. The relationship only works one way: the address can be calculated from the key, but the key cannot be calculated from the address.
When you send crypto, your wallet uses the private key to produce a digital signature. The network checks the signature against your public key and confirms the transaction is authorised — without ever seeing the key itself.
The security model follows from this. There is no password reset, no account recovery, no customer service. Control of the key is ownership. This is why “not your keys, not your coins” is repeated so often: if a company holds the key, you have a claim against that company rather than direct control of the asset.
In practice you rarely handle a raw private key. Wallets present a seed phrase instead, which is a human-readable way of backing up the key material.
For example
A private key is not something you ever type into a website. No legitimate service will ask for it.