"Twitterspeak" is a jargon-laden cant used by heavy users of the social media service Twitter. Twitterspeak is shaped by the various functions and tools embedded within the twitter service, as well as the need to keep "tweets" under 140 characters in length (recently increased to 280 characters). Although twitterspeak can be highly opaque to people unfamiliar with Twitter, some of the terms have spilled over into the broader discourse.
Some examples of twitterspeak include:
@ - prefacing the Twitter handle of another user with an @ sign makes your tweet show up in their mentions. Often used as a verb, e.g. Don't @ me!
DM - a direct, private message to another user
Fav - to mark someone's tweet as a "favorite" by clicking on the "favorite" icon (originally a star, now an exploding heart)
Feed - a running list of all tweets of those you follow, and any tweets your follows have retweeted
Follow - to add someone to your list of users whose tweets will show up in your feed
Hashtag - a tag added to a tweet to add metadata, created by adding a hash mark (#)
Mentions - a running list of tweets in which you were @-ed by someone
Slide into someone's DMs - to hit on someone by following them and getting them to follow you, and then sending them private direct messages
Subtweet - to tweet about someone on Twitter without @-ing them, usually because you are criticizing them
Retweet - by clicking on a retweet icon, you can make someone's tweet show up in the feed of your followers
Thread - a series of tweets replying to each other one after another to build a longer narrative
Tweet - both a noun and a verb: the act of tweeting a tweet, as well as the tweets that are tweeted