BIP39 means Bitcoin Advancement Proposal 39. The words are picked from a certain list of 2048 prevalent English words which can be used to the make a binary seed (your non-public key). If you're Not sure about a certain word's spelling, use the search purpose (Ctrl+File on Windows/Command+File on Mac) https://bookmarkworm.com/story18781690/fascination-about-invalid-bip39-phrase