Pagespeed or mod_pagespeed is an open source module used in apache & is used to speed up the websites. It applies various layers of filters to all the associated assets like pages, stylesheets, images etc, which than helps in optimizing the assets & this leads to boost in speed of the website. The best part of using mod_pagespeed is that, no changes modifications/changes are required to the current existing content. So changes are done at the server side & users accessing the website are presented with the modified content.