What is the difference between confidence and overconfidence?
Usually, confidence is based on experience; proven results with regards to a task or ability increase one's belief that the task can be completed a second time.  Notice that this has nothing to do with what others believe you can do - it's about what you believe you can do.

Overconfidence is bravado - false posturing to fool or mislead others; most often used to hide an actual lack of confidence.  This is all about getting others to believe that one is capable of a task.

There are a lot of non-scientific articles related to the difference between the two concepts:
Here is a "10 characteristics of" page from Hindustan Times
while here is an article from National Geographic talking about narcissism and overconfidence.  

These were found with a Google Search for 'overconfidence vs confidence'.  I'm sure you would get more scientific results if you dig some digging, or tried Google Scholar.