Twitter Language

tweets: Messages in Twitter (max 140 character)
twitter alphabet soup : The Twitter characters with special meaning are: @, d, RT and #:
@: Talk publicly to another person
d: Talk privately to another person
RT: Repeat another person's tweet
#: Tag a message with a label
It all started with the @reply … and then it got complicated. Twitter users started the use of @username at the beginning of a Tweet to indicate a reply. While the Tweet-specific language is always expanding the current elements consist of:

1. @reply – This is a Tweet which begins with @username. This is distinct from the presence of @username elsewhere in the Tweet (more on that in a moment). An @reply Tweet is considered directly addressed to the @username and only some of your followers will see the Tweets (notably, those who follow both you and the @username).
2. @mention – This is a Tweet which contains one or more @usernames anywhere in the Tweet. Technically an @reply is a type of @mention, which is important from a parsing perspective. An @mention Tweets will be delivered to all of your followers regardless of is the follow the @mentioned user or not.
3. @username/list-name – Twitter lists are referenced using the syntax @username/list-name where the list-name portion has to meet some specific rules.
4. #hashtag – As long has there has been a way to search Tweets* people have been adding information to make the easy to find. The #hashtag syntax has become the standard for attaching a succinct tag to Tweets.
5. URLs – While URLs are not Tweet-specific they are an important part of Tweets and require some special handling. There is a vast array of services based on the URLs in Tweets. In addition to services that extract the URLs most people expect URLs to be automatically converted to links when viewing a Tweet.

NOTE: An opensource JAVA API is available to extract these fields. It is available here.  

Twitter hashtag - A hashtag is a way to unite global Tweets around some particular topic. Basically, these are tags that that help those who seek similar content discover your Tweets. According to the official source:

Hashtags are a community-driven convention for adding additional context and metadata to your tweets. They’re like tags on Flickr, only added inline to your post. You create a hashtag simply by prefixing a word with a hash symbol: #hashtag.

Hashtags are getting more and more popular (despite the fact some people are against them wishing their Twitter stream to be metadata-free and “as human a form of communication as possible”)

Twitter Lists - Some details about Twitter Lists:

• Each List is currently limited to 500 people. 
• Each user can create a maximum of 20 Lists. 
• You can create public or private Lists. 
• List names cannot begin with a numerical character. 
• You can add people to Lists without following them. 
• You can add followers to multiple Lists. 
• You can remove yourself from a List by blocking its owner. 
• You can mention any Twitter List as you would any Twitter user, just add a forward slash “/” followed by the list name to list owners username: @/