A tweet which is re-posted is known as a Retweet. It allows you to share a tweet with all your followers. You can Retweet other's tweets as well as your own tweets. Some people type "RT" at the beginning of a Tweet when they re-post someone else's tweet. Although it is not an official command of Twitter, it is used when someone quotes another person's tweet. The purpose of a retweet is to forward information such as news, quote, a website link, to your followers without typing a new post.
Twitter allows turning off retweets for a specific account if you don't like what they share. You are required to choose "Turn off Retweets" from the account profile page. Once you do this, you no longer see the tweets retweeted by these accounts. You cannot remove Retweets that are already in your timeline. One more thing to remember is that you can't turn off all retweets from all accounts. Furthermore, you can no longer see a Retweet if it is deleted by its author or author's account is suspended or deleted.