What's in a tweet? To start, 140 characters, including spaces. Then there are the acronyms, symbols and Twitter-specific lingo that could look like alphabet soup to the uninitiated. Twitter started trading publicly this morning, so you might be wondering what the service is about. Here's a glossary of some of the most common Twitter terms you might encounter, defined in 140 characters or less.

  • Tweet: That 140-character message sent out on Twitter. Also, the sound a small bird makes.
  • Follow: Find an account you like? Click "follow" to have their tweets show up in your feed.
  • RT: Stands for retweet, or resubmitting someone else's tweet to your followers.
  • HT: Hat Tip, means you are sharing a link or idea someone else shared first, so you're giving them credit. Not quite a retweet.
  • DM: Direct Message, a private message sent to another user. You can send it only to people who follow you.
  • @: Add before someone's name to reply to them publicly. It's only shown in the feeds of those who follow both of you.
  • Egg: Unless you upload a profile photo, an egg will show up in its place. Often a sign of a spam account, or someone new to Twitter.
  • #: Hashtags are a way to make posts searchable by topic. Just insert in front of a word, but these days #-less words are indexed, too.
  • FF: Follow Friday, Twitter tradition where users recommend other accounts that people should follow. Happens on Friday.
  • Trends: Popular topics people are talking about on Twitter at any given time, but not the most popular ever. Can change based on location.
  • Promoted tweet, account or trend: Advertisements. Distinguished by an orange arrow and the word "Promoted" next to a tweet, trend or topic.