What is a .abbu file? And what do I do with it?

There is a file that has appeared on my desktop with the following name: "Address Book - 2010-02-22.abbu". If I double click the file, I get a dialog box that says "Are you sure you want to replace all of the contacts in your address book with the contacts in "Address Book - 2010-02-22.abbu"? If you click Replace All, the information in this Address Book archive completely replaces the information in your address book. You can't undo this action."

What is this file? Can I put it in the trash or must I keep it? And if I must keep it, where is its proper place?

Thanks!