BIP39 means Bitcoin Advancement Proposal 39. The words are chosen from a selected list of 2048 frequent English words which may be used to the generate a binary seed (your personal key). If you're unsure about a selected word's spelling, use the research functionality (Ctrl+F on Windows/Command+File on Mac) within https://ledbookmark.com/story4804602/facts-about-bip39-seed-phrase-word-list-revealed