Bip39 Last Word Checksum. From this point forward the seed can be prepared on paper or spoken above phone and this opened up new, physical means of backing up the seed (many paper copies in several destinations, sturdy copies on steel plates with added protection from fire/flood and many others.). https://mylittlebookmark.com/story4144194/bip39-all-words-the-greatest-guide-to-bip39-word-list-numbers