Bip39 seed phrase https://go.bubbl.us/ebe220/f17a?/Bookmarks Although it works by using BIP32 process you can however import BIP39 seeds into Electrum wallet. Also other than BIp32 There exists BIP44 Edition which some wallet use for the generation of seeds. For words that only have three letters, there is not any 4th letter. https://socialrus.com/story21136478/bip39-java-the-5-second-trick-for-bip39-compatible-wallet-https-t-me-bip39-chat