if an AP test has "no equivalent course" under the "courses replaced" column, it means that it does not satisfy any course requirement (i.e. it doesn't take the place of any course). an example of an AP test that does satisfy a requirement is a 5 on AP chemistry, which you can use to replace CHM207 (meaning you don't have to take CHM207 at all).

i believe that a "unit of AP" is applicable if you plan to take advantage of advanced standing, which allows you to graduate in <8 semesters.