Negative training refers to emphasizing the eccentric or negative part of the contraction. This can be a great tool for reducing momentum that you might be using to help you and to break past plateaus you may have reached in your training. Typically, you lift the weight for 1-2 seconds and lower it for 2-4 seconds. In eccentric or negative training, you would still lift the weight for 1-2 seconds but would take 8 to 10 seconds to lower it, thus forcing the muscle to control the weight in a different part of the movement.
I didn't exactly leap out of bed this morning eager to have my butt kicked but I felt great when I was done. Workout? Check!