It generally has bass so low and hard that it has been known to physically damage things. There are no vocals, no soul-just very hard, very fast music. Oftentimes gabber uses 'terror' samples, of death, murder, beatings. The essence of techno music is that it is in a constant state of flux. Every day a new style is created, old things are combined in different ways, and new things are invented.
DJs mix two different tracks and a new song is created.
This is the essence of rave music. It feeds and grows on itself. It is a constant process of mirroring things in on themselves to create an entirely new thing that is combined with something else to create a new thing, etc. So, we get to the dancing. Dancing is, to an extent, yet another reiteration of the music.