"twitter tool." Term used to describe annoying people who use Twitter mainly for marketing purposes or for spamming others with links to their own products/services. See webcock.
It was unintentionally coined by Guy Kawasaki on a blog post titled "How to Use Twitter as a Twool," where he outlined the steps for using Twitter to market your own stuff. People who follow this advice will think they're using "Twitter as a tool" (a twool) when in fact they have become twools themselves.
"Ugh. All this guy does on Twitter is pimp his SEO business. What a twool. UNFOLLOW"