Sometimes broad match keywords are, well, a bit too broad. When that's the case, we add keyword modifiers to your keywords in order to tell Google that the search term must include that word in order for your ad to appear. If you see a + in front of your keyword, that means keyword modifiers have been added.
Example: If your keyword is "+apartments in +Center +City +Philadlephia", the user must include "apartments", "Center City" and "Philadelphia" in their search in order for your ads to appear.
Next, learn about keyword match types.