What's the difference between a retweet and reply? A retweet looks just like a reply with a quote of what was replied to. Is there anything else different.
If you are following someone on Twitter and they tweet something you want to share with the people following you, you retweet. This reposts the tweet onto your timeline and makes it possible for your followers (who may not be following the original tweeter) to see the tweet.
If you are following someone on Twitter, they tweet something and you reply to that tweet, the people following you can see your reply, but they don't know what the original tweet said.
If you choose to reply with a quote, then the original tweet will appear in your timeline as well. (Not all Twitter apps will allow you to reply with a quote.)
There is no difference between an "old school" retweet and reply except the existence of the conventional "RT" and usually retweets didn't add any additional commentary.
Recently Twitter changed to have Retweets be their own very special sort of Tweet. Gone is the "RT" of old, but now one can easily find the Tweets that one has Retweeted or had Retweeted.
More information can be found at the Twitter FAQ.
Let me try some examples.
If we assume twitter as a mailbox, then a
retweet would be a forward mail. A forward mail just some nice photos, jokes or some other interesting things which you got from someone and forwarding it to your contacts.
In the same scenario, if you reply back to that forward mail or some other mail which has been addressed to you it can be compared to a
reply on twitter.
Now, those are what
retweet mean. Visually, old style retweet (refer Al's answer for old and new retweet styles) and reply are almost the same except the RT. Many people prefer the old style retweet as it allows you to comment/reply while you RT it.