BasicCrypto1 min
A seed phrase (recovery phrase, mnemonic phrase) is a set of usually 12 or 24 words from which all the keys and addresses of a crypto wallet can be restored.
In plain words
Whoever knows the phrase fully owns the wallet. Whoever loses the phrase together with the device loses access for good: support cannot restore it. So write the phrase on paper or metal, do not photograph it or keep it in the cloud or in notes, never tell it to anyone (wallet support will never ask for it) and keep the words in the right order.
Example. The phone with your wallet breaks: you install the same app on a new phone and enter the 12 words in the right order, and the balance and addresses come back.