What is ska music?

I know that some ska bands are The Mighty Mighty Bosstones, No Doubt and Reel Big Fish, but what exactly is it?
Sam

Here are some proper ska bands

Desmond Decker
The specials
Judge Dread
The Beat

Ska like what the person before me said is like regge and punk it was born in jamecia when the started gettin electric guitars and new tecnolodgy , but was reinvinted in england in the 1970s , you would commenly see skinheads dancing to the same bands as the black english people , it was a real movement and in a turbelant time brang people together from all walks of life like no music I have ever heard of .

its like reggae but with a bit more of a punk feel to it