This directive lets Apache adjust the URL in the Location header on HTTP redirect responses. For instance this is essential when Apache is used as a reverse proxy to avoid by-passing the reverse proxy because of HTTP redirects on the backend servers which stay behind the reverse proxy.
<path> is the name of a local virtual path.
<url> is a partial URL for the remote server - the same way
they are used for the ProxyPass directive.
Example:
Suppose the local server has address
http://wibble.org/; then
ProxyPass /mirror/foo/ http://foo.com/ ProxyPassReverse /mirror/foo/ http://foo.com/will not only cause a local request for the <http://wibble.org/mirror/foo/bar> to be internally converted into a proxy request to <http://foo.com/bar> (the functionality ProxyPass provides here). It also takes care of redirects the server foo.com sends: when http://foo.com/bar is redirected by him to http://foo.com/quux Apache adjusts this to http://wibble.org/mirror/foo/quux before forwarding the HTTP redirect response to the client.
Note that this ProxyPassReverse directive can also be used in conjunction with the proxy pass-through feature ("RewriteRule ... [P]") from mod_rewrite because its doesn't depend on a corresponding ProxyPass directive.