Can someone explain Twitter Speak to me?

[David C]

The at-sign is used to introduce the name of a user. It will produce a link to that user's page, and they will be able to see that you referenced them. So a tweet "Saw @wilw on Eureka" would refer to Wil Wheaton's account, provide a link to him, and let him know he had been mentioned.

If the reference to the user is the first thing in the tweet, then it is treated as a reply to that person, and can only be seen by you, him or her, and people who follow both of you. (Normally when you make a tweet, it can be seen by anyone who follows you.)

To avoid the tweet being limited to people who follow both of you, people will often put a period at the beginning: ".@wilw was on tonight's episode of Eureka. Cool!"

RT means "retweet". It is when you rebroadcast something someone else already tweeted. Originally, the only way to do that was to retype (or copy and paste) what they tweeted, so people would put "RT @whoever" at the beginning to give them credit. More recently, Twitter has come up with a built-in way to retweet someone else's tweet, so instead of seeing "RT" at the beginning, you'll see square double arrow icon and who it was retweeted by, at the top.

The hash symbol (#) is used to add hash tags to a tweet. The purpose is to give the topic, or category, so that people can search for information by topic. People come up with these tags in a completely ad hoc way. There aren't any "official" tags. Just make them up:

.@wilw was really awesome on Eureka yesterday. #syfy #eureka

But because people can put anything they want as a tag, they sometimes put things that aren't so much anything anyone would actually search for, as just a sarcastic, ironic, or humorous comment on the preceding tweet:

My stupid roommate hid my car keys behind the couch. #notreallythatfunny

I don't know what the < symbol is for. Haven't seen that one. Maybe someone else can tell you.