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.
<BlkNoOne> im going to see type o tonight