Some basic definitions: Intervals

More terminology of training.

First we need a few terms to help with the definitions.

Work is when you are actually exercising. Lifting the weight, sprinting, jumping, etc. - it's all work.

Rest is when you are either not exercising (taking an actual break) or when you are doing a light, non-strenuous exercise to facilitate recovery from work (such as walking around, or jogging instead of sprinting). What counts as rest depends on how high the perceived intensity is - if walking is non-strenuous, it could be considered rest. Generally anaerobic exercises - like pushups, pullups, etc. aren't "rest."

Now that we have those, let's talk about intervals. These generally apply to "cardio" training but not exclusively.

Interval Training (IT) is when you alternate periods of work with periods of rest, usually in a specific time ratio. For example, if you sprint for 30 seconds and then jog for 120 seconds, you're doing sprinting intervals with a work:rest ratio of 1:4. Generally rest intervals range from 1:1 (lots of work!) 1:5 or more (lots of rest!) but they vary considerably. If there is no work:rest ratio - you just continuously do the same speed, this is not IT but rather steady state exercise.

HIIT (High Intensity Interval Training) is a subset of IT. This is usually interval training with a work:rest ratio of 1:1 to 1.2.

Tabata Intervals are a subset of IT or HIIT. They are named after Dr. Izumi Tabata, who showed in a lab test that 8 rounds of 20 seconds of cycle sprints with 10 seconds of slow cycling (a work:rest ratio of 2:1) burned off more body fat than 45 minutes of steady-state cycling...and that was without most of them being able to complete all 8 rounds. Tabata intervals ("Tabatas" for short) can be done with any fast, repetitive cardio exercise or lift. Examples include sprinting alternated with jogging, bodyweight exercises (pushups, pullups, or squats) alternated with rest, kickboxing rounds...you can let your imagination go on these.

Useful links
For more on Intervals:
http://en.wikipedia.org/wiki/Interval_training

For more on HIIT:
http://en.wikipedia.org/wiki/High-intensity_interval_training
http://www.exrx.net/ExInfo/HIIT.html

For more on Tabatas:
http://www.rosstraining.com/articles/tabataintervals.html