Bip39 light standard https://devinzryy552.trexgame.net/comprehending-bip32-vs-bip39-which-one-should-you-make-use-of Although it makes use of BIP32 process it is possible to nonetheless import BIP39 seeds into Electrum wallet. Also apart from BIp32 There's BIP44 Edition which some wallet use for that generation of seeds. For words that only have 3 letters, there isn't any 4th letter. https://cheapbookmarking.com/story20375080/bip39-seed-phrase-the-smart-trick-of-bip39-word-list-github-that-no-one-is-discussing-https-x-com-tundra838554