A real-life meeting organised on the social networking web site Twitter.(noun)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "tweetup" in a sentence
"Even though this tweetup is by invitation only, if you are heading down to the Airshow this Friday from 3.30 – 5. 00pm (which means you have an Airshow trade pass), be sure to pop by the tweetup venue."
"But yes, calling it a tweetup is a bit off I think."
"But after that there's a get together downtown (aka tweetup)."