It's a type of workout where you alternate bursts of energy with periods of recovery. There are many variations of interval training. If you want cycling specific intervals, you could try "The Time Crunched Cyclist" by Chris Charmichael. The book is primarily about training for Centuries or racing, but if you follow the methods, you'll get into great condition. Interval training is an excellent cardo workout and a great alternative to jogging.
One popular method of interval training is the "Tabata" method. This uses 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max or 90 - 95% of your max heart rate) followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles). Typically, this is done 3 or 4 days a week and not on consecutive days.