Re-Tweet: To post a copy of someone else's tweet on your own account.
Example:
If I were to post the following on my Twitter account...
The Periodic Table of Awesoments: very scientific, stupid-awesome -- http://shrt.st/ve...and if you were to really like it and want to post it as well, you could do so as long as you give credit to the original tweet.
An easy way to do so is to format your tweet like this:
"Re-tweet @netizenbane: The Periodic Table of Awesoments..."
By beginning with the word "Re-tweet" you are telling your followers that you're posting something that you found interesting from someone else. You're also giving your followers the opportunity to check out the original Twitter user's profile in case they find that person's posts interesting and choose to follow them as well.
Why do so?
Twitter is a community. Like other "Web 2.0" sites, Twitter depends on the input of its users to drive not only its content but also its relevance. If the community doesn't thrive, Twitter doesn't thrive. And communities thrive best when their members have at least a basic set of understood guidelines for behavior.
This is not to say that such guidelines are meant to restrict your use of this service. On the contrary, such guidelines are meant to enrich your experience!
So while you're learning the ropes, I'll continue to toss in any relevant behavioral tips. Feel free to use them as you please. In my opinion, the single-best piece of behavioral advice can be found at Wiki-Media's meta site under this heading:
Enjoy Re-Tweets responsibly,
~Chucklyn