This technique comes from Pierre Roy, one of Canada's best strength coaches. It involves doing the same exercise twice in one workout. So whatever you are trying to improve do it two times in the workout. So if your trying to better your back, then do back work at beginning, and then again at the end.
For example- Do 6 sets of back at the beginning, go do your other part of your workout, and then come back and do 6 sets of back at the end.
**** I have also used this technique another way to promote hypertrophy. What I do is an exercise first, then another exercise for the same muscle group, and then finish with the first exercise. This really puts a hurt on your target muscle.
For example- 10 reps of decline tricep extension, then 6 reps of dips, and then back to the tricep extensions for 10 reps but with less weight.