Click Ignore All in the menu, and Word will ignore all the errors of this string in the current document. Click the Add to Dictionary command, and Word will add the string to the random dictionary. When you enter this string in the document in the future, there will be no error prompt.

An underline with a green waveform indicates that there may be a grammatical error, which is handled in the same way as the "spelling error" above. Red and green wavy underscores represent errors.