A recovery phrase, also called a seed phrase or mnemonic, is a sequence of 12, 18 or 24 words that can restore your entire wallet. It is the human-readable form of your private keys.
Your wallet derives every private key from this phrase using a standard called BIP39. Anyone who has the phrase controls every account derived from it, on every supported chain.
If you lose your device, the recovery phrase restores your funds. If someone else gets it, they can steal everything. It is both your backup and your single biggest vulnerability.
Write it on paper or steel, never store it digitally, never type it into a website or app, and never share it with anyone, even someone claiming to be support.
Your recovery phrase is the most important piece of data you own in crypto. Protect it accordingly.