Whiplash is pretty dead on. I'll just add a few other random thoughts...
AOR - Mellower...either feel-good or heartache, not deep. Often over-produced by big names to get as many tunes as much airplay as possible, "studio/FM-oriented" bands. Best example: Journey, REO Speedwagon, Foreigner.
Sleaze - Basically Hard Rock that doesn't care about image, lots of sexual innuendos, live performances often degenerate before your eyes, "club-oriented" bands. Best example: Guns N Roses, L.A. Guns, Faster Pussycat.
Glam - Also Hard Rock but all about appearance, while combining the sexual innuendos of sleaze with the love and heartbreak of AOR, front man preferrably pretty to help sell albums to teenage girls, men often dressing like women, "video-oriented" bands. Best example: Poison, Cinderella, Britny Fox.
Prog - Trying to combine unorthadox sounds with deeper lyrics, an attempt to move mainstream music in a different direction, "artistic-oriented" bands. Best example: Dream Theater, Fates Warning, Marillion.
Hard Rock - Like Whiplash states, emphasis on lead guitar, with rhythym guitar or keys helping. Elements of teen rebellion, fantasy, and love (in the form of power ballads). Powerful singers to avoid being drowned out by the guitars, breakups usually involve power struggle between singer and lead guitarist, sound made to be transferable from studio to big concert productions, "stadium-oriented" bands. Best example: Van Halen, Judas Priest, Dokken.
Obviously some bands have multiple traits, and some have multiple incarnations. Just my take...