Answer
A blue wavy underline is a "possible word choice error." It means that the text is both grammatically correct and correctly spelled as is, but that Word thinks you might have intended a different word anyway.
A number of common typing errors result in apparently correct phrases that are not what was intended by the writer; these can be difficult to capture with spelling and grammar checkers, which confirm that the sentence apparently obeys the rules they have been given and move on, unaware that the sentence is nonsensical or incorrect.
Microsoft has identified some of the most common errors of this type, and flags them in blue, so that you can check and confirm that they are not errors.
Some examples (from the text I'm currently editing):
"Some ale to quench your thirst" (in the context "ale to," Word suspected I might have meant "able to.")
"to bind you" ("bind" and "find" are both verbs, but "find" is by far the most common, so Word highlights it as suspect.)
"No, sire" ("sire" and "sir" are both direct forms of address, but "sir" is much more common than "sire," so again Word highlights it.)
Chat with our AI personalities
Exampler for this is type:We go to school with all there friends there got
blue underline. That means the word pair like their or there.If you place the wrong one it causes blue wavy lines