Double blue lines in Word
OK, I found the reason why it's highlighting it. As @LPChip noted, it's just pointing out that it's kinda wordy. To fix it, I just right-clicked my word and selected the suggestion in the menu.
I was able to get rid of some of the double blue underlines by unchecking "wordiness" in the preferences. I went to Word-->Preferences-->Spelling & Grammar-->Settings button (under Grammar section) and unchecked Wordiness. It's still appearing for some other errors, but at least it's not appearing as much.