Hanging out on Twitter can be pretty fun, but there are a lot of abbreviations to get your head around.
You may be familiar with the most common, "RT", which is to retweet someone's message. But there's also "MT", which means the tweet has been modified or paraphrased from the original.
"DM" is a direct message to privately talk to someone without your whole stream watching. "HT" is to give someone a hat tip to thank another Twitter user or give them credit. And "CC" is just like email: carbon copy, or to bring a tweet to another user's attention.