I’m not really deep into theory of jazz or anything, in my understanding “Hard Bop” (or “Hard Bebop”) is more intense, rhythmic, and has significantly extended solos compared to just “Bop” (or “Bebop”) Jazz. There is more about this on wiki, but I personally find it easy to hear the difference intuitively after hearing some bebop and some hard bop works. The main source to dig for classics of this genre is a label called “Blue Note”, but it’s huge and features a lot of other styles of jazz. I personally discovered this genre from a work called “Bolivia” by Cedar Walton. It’s also hard bop, but it’s not guitar driven.