What is a proxy server?

You can have a look to the software CCProxy or Squid.

Good topic.. I'll tell u in simple about proxy server.. It is just an application tat is inbetween the client or browser and the main server.. the client requests will pass thro the proxy server.. and the proxy sees whether if itself can answer to the request of client, it does it.. else, it forwards the request to the main server.. Tis is to minimize the request to be handled by main server.. cuz main server will always have more no of requests n works to be done.. so, by using proxy's we can minimize the work load on main server.. proxy's can also be used to filter or block certain requests.. eg: in companies chat appln's are all blocked by using proxys.. and using proxys only the users access chat applications without the knowledge of the company.. hope its clear for u..

I'm really not sure what it is but I'm gonna take a guess. I think a proxy server is a server that can connect to any server in order to view any website without really being on it's server. If I had 500 posts i would just copy the entire definition outta wikipedia but I don't. Oh and that was just a guess. I'm sure you'll find the exact definition at http://wikipedia.org/wiki/proxy