BIP39 means Bitcoin Advancement Proposal 39. The words are chosen from a certain list of 2048 frequent English words which can be used to the deliver a binary seed (your personal important). Standard recovery phrases use a certain list of 2048 words subsequent the BIP39 standard (Bitcoin Improvement Proposal 39). https://bookmarksoflife.com/story4376208/a-secret-weapon-for-bip39-words-to-numbers