Online jargon used to describe a forward slash in a URL. When describing an Internet address at Microsoft, for example, you will commonly hear "http colon whack whack dub-dub-dub dot microsoft dot com whack partners" which translates to "http://www.microsoft.com/partners". Apparently it is also used, at times, to describe a back slash as well.
An older definition of "whack" according to arch-hacker James Gosling, is "To modify a program with no idea whatsoever how it works." In this definition, it is a "whacker" who is doing the "whacking."
Thirdly, another definition of whack as specified in M$spec, refers to the path name on a server, which leads to a UNC joke of server Patty having a resource named GiveYourDogABone: What's the mapping to it? PattyGiveYourDogABone} (That should give you a real taste of geek humor.)