A superset is when two or more exercises hitting different muscle groups are performed in a row without rest between them.
It's great to superset when strength training body parts that require a lot of rest between sets.
For instance, when squatting heavy, you might normally take 2 minutes of rest before doing your next set, but in supersetting you might use that valuable 2 minutes of gym time to do another exercise, like bench pressing. That way, you can bang out a chest workout while your legs recover. Then, as your chest muscles get ready for the next bench press set, you can bang out a set of squats!
Another reason to superset is to build up muscles that are opposing each other but use different exercises for the main muscle group.
For instance, it's common to superset biceps and triceps exercises, alternating between curls and rope push-downs. While the larger muscles of the biceps and triceps are on opposing sides of the arm, the two muscle groups still have to work together. The end result is a monster-sized, double pump on some of the overlapping muscles!
Many people will also superset chest and back exercises for both of the above reasons. While longer rest periods are often needed between sets of bench press lifting, the back and arm muscles are also slightly hit, so it makes sense to throw in some pull-ups for a superset!
Here's a two-week sample of superset exercises you can try adding to your workout routine, hitting the muscle groups of the back and chest. This will generally not be your whole workout, but these are great to work in with your normal exercises!
You can also try these supersets when you're really crunched for time. If you only have 30 minutes to hit the gym some days, supersetting is an awesome way to maximize that window.
Some of these exercises can be switched out for others. Feel free to use a different lift in your workout that works the same muscle group.
Try experimenting with back-to-back upper-body and lower-body exercises, like deadlifts and push-ups to exhaustion, for insane energy expenditure and fat burning.
Or, try switching between three exercises, with your first exercise being front squats with either dumbbells or a barbell, your second exercise being overhead presses with dumbbells, and your third being a chest exercise like pec-focused dips.
When you start doing supersets, you'll find that your endurance may be a problem as you go from exercise to exercise, but before long you'll learn to love these workouts.
You'll probably see a huge muscle pump from working some of the overlapping muscles at the same time, and you'll totally appreciate the way you've maximized your workout time.