A seed phrase is a series of words generated by your cryptocurrency wallet that give you access to the crypto associated with that wallet. ... Think of the wallet as being like a password manager for crypto, and the seed phrase as being the master password.
Master as in the MAIN password that will get you into your wallet in the case of losing your secondary sign-in password.
Example of a MetaMask Seed Phrase:
Monkey avalanche tree snake mountain goat backhand play grocery other bag report
Whenever you are given a seed phrase you should copy it down on a piece of paper, and put it in a safe place. It would be wise NOT to take a screenshot and save it. It would also be wise NOT to give it to anyone because this is the gateway to your crypto wallet and all of your money.
For a deeper dive on seed phrases, please watch the video below with Alex from nfts.tips.