what is "re-tweeting"?

[site]

[Peter]

Reposting something on Twitter.

[TheVoiceOfReason]

I believe is is copying something somebody else already tweeted into one of your tweets but I could be wrong

[Holly]

A re-tweet is when you post something on your Twitter profile that you saw on someone else’s. The purpose of a re-tweet is to share with your community something that you learned or found interesting. The proper etiquette for a re-tweet (RT) is to say RT @their user name:___ repeat their message.

[Rose .]

A retweet is when you re-publish something another Twitter user has written, to spread the word among your own Twitter followers. Things you might want to retweet include sweepstakes announcements, links to helpful articles, or breaking news - in short, whatever you think your Twitter readers might like to hear about. Retweeting causes a ripple effect, helping more people hear about an interesting Tweet. Many times, you will need to retweet posts from sponsors to enter Twitter contests.
You designate a retweet using the abbreviation RT followed by the original Twitterer's name and message. For example, RT @ContestsGuide would indicate that you are retweeting information that I originally posted. So to retweet, type the following into Twitter and send:
RT @twitterusername text of the original message.

:o)