Interval, or intermittent training alternates intense activity with lower intensity activity. A common misconception is that in order to get a better workout you have to participate in a high-impact activity for an entire hour. Not true. You'll burn more calories and increase aerobic endurance by doing interval training. I do this in Zumba® classes by manipulating impact, tempo, intensity, and traveling during songs. By this I mean you have the option to jump higher, drop lower, and/or travel farther to increase the challenge of your workout with me.
I design playlists for my classes to both increase heart rate and increase endurance. Doing a movement more slowly, with a bigger range of motion takes more strength than doing that same movement quickly. So if you come to one of my classes, you'll find yourself doing both fast and slow songs that are put into the playlist with intention.
Here is a good article on the subject.