@reply: A direct tweet sent to another Twitter user visible by others following either the sender of recipient.
DM: A direct tweet only visible by the recipient.
Dweet: Tweet sent while drunk.
Hash Tag: The “#” sign. Allows Twitter users to group tweets by topic, making it easier to search particular conversations using Twitter Search.
Link: Including a URL in your tweet.
MisTweet: A tweet one later regrets.
ReTweet: To repost something that’s already in the Twitter stream. Usually preceeded by “RT” and “@[username],” to give credit to the original poster.
SnapTweet: A tweet that includes a photo taken with a cell phone, uploaded to Flickr and posted to Twitter via snaptweet.com.
Twittcrastination: Procrastination brought on by Twitter use.
Twadd: To add someone as a friend or follower.
Twebay: To sell something on Twitter.
Tweeter/Twitterer: Someone who uses Twitter.
TwinkedIn: Inviting friends made on Twitter to connect on LinkedIn.
Twittectomy: To remove someone from the list of people you follow.
Twitterati: The A-list twitterers everyone follows.
Twitterfly: Twitter’s version of a social butterfly, marked by the extreme use of @ signs.
Twitterlooing: Twittering from the bathroom.
Twitterpated: Overwhelmed with Twitter messages.
Twittfeinated, Twigged Out, Twired: To be so hyped up on twittering that you cannot sleep.
Data: Twitter Fan Wiki