The Word function that corrects text as you type is referred to as Auto Correct.
Text replacement, replace-as-you-type or autocorrect is an automatic data validation function commonly found in word processors and text editing interfaces for smartphones and tablet computers. Its principal purpose is as part of the spell checker to correct common spelling or typing errors, saving time for the user.
Choose AutoCorrect options for capitalization, spelling, and symbols. You can use the AutoCorrect feature to correct typos, capitalization errors, and misspelled words, as well as automatically insert symbols and other pieces of text.
Auto-correct is a type of software program that identifies misspelled words, uses algorithms to identify the words most likely to have been intended, and edits the text accordingly. Auto-correct is commonly a feature included in word processors and messaging platforms of various types. Apple, Google and Microsoft products all have their own versions of auto-correct programs.