Over time Twitter, or more accurately, Tweets have acquired a unique lexicon of their own. Some of the vocabulary has been around since the dawn of Twitter — like @username at the beginning of a Tweet — whilst others are relatively recent — such as lists — but all of them make the language of Tweets unique.

What are the Tweet-specific elements? According to Twitter:

• @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).
• @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.
• @username/list-name — Twitter lists are referenced using the syntax @username/list-name where the list-name portion has to meet some specific rules.
• #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.
• 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.

Other important syntaxes found in a Tweet

• RT @username — This is known as a Retweet. Similar to @mention, this type of Tweet refers to when a Twitter user is forwarding a Tweet, from another Twitter user, to their own followers. In essence the Tweet is being re-broadcast (generally without any editing).
• D @username — This is known as a Direct Message. Direct messages are similar again to an @reply, however, there is only one recipient of the message. The D @username element must appear at the beginning of the Tweet and only the referenced @username will be sent the message.
• via @username — Much like retweets and therefore similar to an @mention, this type of Tweet refers to when a Twitter user is forwarding on a Tweet, from another Twitter user, to their own followers. The Twitter user forwarding the Tweet may have edited the original, but out of courtesy have mentioned the originator.
• QT @username — This is known as a Quoted Tweet. It’s not often used outside Japan but is in essence a retweet.
• ^ (Co-Tag) — Known as a Co-Tag or sometimes a cotweet, this syntax appears when more than one person has access to a specific Twitter user account. It is a form of signing. For example, if I were to contribute to a corporate Twitter account, I may sign-off as ^SW (my initials).
• cc @username — Very much like an @mention, the carbon-copy syntax is a relic of the email world, but is useful for highlighting to a specific Twitter user a Tweet, whilst not necessarily directing the content of that Tweet to them.