Usually twelve or twenty-four words, it is the master backup for a self-custody wallet. Written down and stored offline it is robust; photographed, typed into a website or stored in cloud notes it is a liability.
No legitimate service, exchange, wallet or publication will ever ask for it. Every request for a seed phrase is an attempt to steal from you, without exception.
This definition is educational and not financial advice. Crypto is volatile and high-risk — always do your own research.
Keep learning
New to crypto, or filling in the gaps? Work through the essentials in Learn, browse every term A–Z, or see live prices for the coins these concepts power.