grunge -- commonly used to describe a type of rock that's somewhat on the heavy side. throaty voices and guitars with heavy gain and bass are common.
metal -- the heaviest form of rock. the music is sometimes classified as angry, often with screaming or growling voices incorporated, as well as drums with double bass, heavy guitar progressions in a minor key, high gain lead guitar solos, and a fast tempo. metal even has its own subgenres, such as death metal (commonly the music associated with the style generalization of "goths"), hair metal, melodic metal, etc.
punk -- debatably the fastest paced form of rock. often the music is simple, consisting of power chords and simple lead guitar parts very frequently in a major key, and simple but fast paced drumbeats with a fill added every so often. punk is sometimes otherwise defined by politically critical lyrics. this is one of the genres used also to classify a certain group of people, who are often automatically judged as immature, skaters, stoners, and pricks.
hardcore -- music that is similar to metal in its heavy components (such as incorporated screaming vocals, drums with double bass, etc.) but with thinner singing voices, a higher pitched and thinner scream, and a rhythm guitar distortion with less gain and bass and more treble. also a term misused to generalize people as tough or fearless, and usually a style with a lot of body piercings is included in...