IRC slang for "word," as in "word to your mother." It originally started in EFNet's #nin, where substituting 3 for e ("w3rd") had become popular leet-speak parlance. At some point, someone slipped up and hit the f key (note its close proximity to the "r" key), and it caught on. It has since propogated throughout the IRC community.

When you eat dirt for the first time and leave your family to build a shack in the woods