If it's in the same folder as your .wab file (Windows Address Book) - then it's just a temporary file of the address book from before the last change to it. It's quite handy as a backup, so best leave it there.
the ~ suffix on a file usually means that a program has created or modified a file with a name longer thatn it can use so it cuts the name short and replaces the end of the name with ~ it's just like any other file and should be deletable james
this file is a dump file automatically created in the event of a system crash or similar event. you can use it to help with debugging, if you know how, after a system failure but it is not a system file and is also not essential to make you're computer work so yes you can delete it if you need the space. james