BIP39 means Bitcoin Improvement Proposal 39. The words are chosen from a certain list of 2048 common English words that may be used to the generate a binary seed (your non-public key). Standard recovery phrases use a selected list of 2048 words pursuing the BIP39 standard (Bitcoin Advancement Proposal 39). https://socialmarkz.com/story9419788/top-guidelines-of-bip39-word-list-pdf