Hard rock is a term that's frequently applied to any sort of loud, aggressive guitar rock, but for these purposes, the definition is more specific. To be sure, hard rock is loud, aggressive guitar rock, but it isn't as heavy as heavy metal, and it's only very rarely influenced by punk (though it helped inspire punk). Hard rock generally prizes big, stadium-ready guitar riffs, anthemic choruses, and stomping, swaggering backbeats; its goals are usually (though not universally) commercial, and it's nearly always saturated with machismo. With some bands, it can be difficult to tell where the dividing line between hard rock and heavy metal falls, but the basic distinction is that ever since Black Sabbath, metal tends to be darker and more menacing, while hard rock (for the most part) has remained exuberant, chest-thumping party music. Additionally, while metal riffs often function as stand-alone melodies, hard rock riffs tend to outline chord progressions in their hooks, making for looser, more elastic jams should the band decide to stretch out instrumentally. Like heavy metal, hard rock sprang from the mid-'60s intersection of blues-rock and psychedelia pioneered by artists like Cream, Jimi Hendrix, and the Jeff Beck Group. Blues-rock and psychedelia were both exploring the limits of electric amplification, and blues-rock was pushing the repeated guitar riff center stage, while taking some of the swing out of the blues beat and replacing it with a thumping power. Hard rock really came into its own at the dawn of the '70s, with the tough, boozy rock of the Rolling Stones (post-Brian Jones) and Faces, the blues-drenched power and textured arrangements of Led Zeppelin, the post-psychedelic rave-ups of Deep Purple, and the loud, ringing power chords of the Who (circa Who's Next) setting the template for much of what followed. Later in the decade, the lean, stripped-down riffs of AC/DC and Aerosmith, the catchy tunes and stage theatrics of Alice Cooper and Kiss, and the instrumental flash of Van Halen set new trends, though the essential musical blueprint for hard rock remained similar. Arena rock also became a dominant force, stripping out nearly all blues influence and concentrating solely on big, bombastic hooks. During the '80s, hard rock was dominated by glossy pop-metal, although Guns N' Roses, the Black Crowes, and several others did present a grittier, more traditionalist alternative. Old-fashioned hard rock became a scarce commodity in the post-alternative rock era; after grunge, many guitar bands not only adopted a self-consciously serious attitude, but also resisted the urge to write fist-pumping, arena-ready choruses. Still, the '90s did produce a few exceptions, such as Oasis, Urge Overkill, and the serious but anthemic Pearl Jam.