BIP39 means Bitcoin Advancement Proposal 39. The words are selected from a specific list of 2048 popular English words which can be accustomed to the produce a binary seed (your non-public critical). Standard recovery phrases use a certain list of 2048 words pursuing the BIP39 standard (Bitcoin Enhancement Proposal 39). https://esocialmall.com/story4184964/ledger-seed-phrase-bip39-no-further-a-mystery