It stands for Fascial Stretch Training and the seven refers to 7 sets performed usually as the final exercise of a target bodypart. Basically you train that bodypart on any given day heavy as you normally would keeping the rep range between 8-12, but the last exercise you perform the seven sets to finish off that particular muscle, with minimal rest in between to get the best pump possible.
You should refrain from using compound lifts as your "seven set," because they require balance and the use of ancillary muscles which takes focus off the target muscle. Machines and cables are a good idea and free wights like barbell curls and skull crushers also work well for this "seven set". Perform your "seven set" at the end of the workout for that muscle group.**
The goal is to bring as much vitamins, minerals, amino acids, oxygen etc. into the muscle, and also stretch the fascia surrounding it to help encourage maximal muscle growth. The fascia is the limiting factor in acheiving muscle growth because the mucsle will grow only as much as there is room for it to do so. This training system is targeted to stretch the fascia and allow more room, instead of limiting muscle growth.
** Restricting the "seven sets" as your last exercise is recommended for new users of this training principle. This will allow you to lift heavy for first few exercises before taking the muscle to failure. There are many other variations for advanced users, including "front-loading the seven sets", that will be discussed in the forums and blogs to allow creativity in workouts and to shock and further stretch the fascia and enhance muscle growth.
For sample workouts go to fst-7.com
I have been using this technique every week since I started with Hany. Make sure to give it a try and you will get the fullest pump you have ever experienced!