Ska is a great form of music that can be anything from
light to
hardcore, depending on the
band and the
era. The sound is sort of like a cross between
reggae and
punk, even though it predates both of these. The distinguishing characteristic of ska is that the tune is carried on the
upbeat rather than the
downbeat (in other words, while most
musical styles will have tunes that go ONE, TWO, THREE, FOUR, ska goes one AND two AND three AND four AND.)
Historically, ska has it's roots back in the late 60s and 70s. The style is generally attributed a band called The Skatalites, who first got together in 1964. This band and some of its contemporaries (most notably Desmond Dekker and The Specials) formed the first wave of ska. This wave had really great tunes, which had a toe-tapping beat that made it almost impossible not to get up and dance. The major emphasis was on the horn section.
Ska's second wave (the most notable example of which is the inimitable Madness,) contained more variety of instruments, most notably keyboards and guitar. Music of this wave had a fuzzy boundary at times with the popular punk movement, and so this was the real beginning of hardcore ska.
The third wave of ska has many more factions than the previous two waves, such as California ska and ska-punk. The third wave has elements of each of the two previous waves, with new innovations as well, depending on the band. The guitar and the horns are the most important parts, although this varies from band to band (Goldfinger, for example, has no horn section.) Prominent and popular examples include The Mighty Mighty Bosstones, Reel Big Fish, and Fishbone.