Reverse telephone numbers are regular telephone numbers -- just in reverse.
A better term is "reverse lookup." Let's say that you pick up the phone book, look up "Homer Simpson", and find that his number is "867-5309". That is a forward lookup. A reverse lookup is when you search for "867-5309" and find out that this number belongs to one "Homer Simpson."
Years ago, it was very difficult to gain access to a reverse telephone directory. Now, with the magic of the Internet, you can find them online everywhere. Here are a few:
A better term is "reverse lookup." Let's say that you pick up the phone book, look up "Homer Simpson", and find that his number is "867-5309". That is a forward lookup. A reverse lookup is when you search for "867-5309" and find out that this number belongs to one "Homer Simpson."
I actually did a search on 867-5309, and I see that this number belongs to a Jenny...?