Bip39 Seed. The passphrase is just not chosen in the predefined list of 2048 words – it can be any word or phrase you choose. BIP39 specifies a list of 2048 words from which the mnemonic phrase is chosen. Every single word represents a number in a very binary sequence, https://bookmarklinx.com/story18854137/bip39-word-list-https-linktr-ee-bip39-what-does-ian-coleman-bip39-mean