A “brainwallet” refers to a private key that is stored in the user’s memory in the form of a seed phrase or a passphrase.
Source
Home > News > Bitcoin News > Brainwallets: The Bitcoin Wallet You Probably Shouldn’t Use (Unless You Have To)
A “brainwallet” refers to a private key that is stored in the user’s memory in the form of a seed phrase or a passphrase.
Source