Usually proxies handle outgoing requests from a network. A reverse proxy handles incoming requests to a network.

In this context, a reverse proxy would read the request from a client, ask another Apache httpd instance for the data, then return that data to the client.

This way, the mod_perl server can finish the request quickly and doesn't bog down a process (with a presumably large chunk of RAM) with downloading the response bytes to the client (on a slow connection).