HIIT, or high-intensity interval training, alternates short periods of hard effort with periods of recovery. The recovery is what lets you go hard again, so each work interval can be tougher than anything you could keep up continuously.
The split between work and rest is up to you, and it's the main thing to adjust as you get fitter. Common choices are 30 seconds on and 30 off, 40 on and 20 off, or 45 on and 15 off. If you're new to it, start with as much rest as work, or more.
A session usually strings several moves into a round, repeats the round a few times with a longer recovery between rounds, and finishes with a cooldown. Tabata is one particular kind of HIIT, with a fixed 20 seconds on and 10 off.