BIP39 means Bitcoin Improvement Proposal 39. The words are chosen from a selected list of 2048 common English words which may be used to the make a binary seed (your non-public critical). For anyone who is unsure about a particular word's spelling, make use of the search operate (Ctrl+F on https://mnobookmarks.com/story18881965/ledger-seed-phrase-bip39-no-further-a-mystery