HIT training is High intensity training, it comprises of much shorter weights sessions usually no longer than 45 minutes tops with usually only one set per exercise taken to and often beyond failure. With a lot more recovery time advised. The theory is that muscles growth is triggered by the intensity of the effort not the volume of the work, kinda of like why marathon runners are skinny and sprinters are more developed!
Now you may of meant to write HIIT, which is high intensity interval training! This is a form of exercise where you switch back and forth between periods of low intensity exercise and high periods! For instance 20 seconds high and 40 seconds low for 15-30 minutes. Often done with cardio exercises but can been done with weights and circuits. The theory is that you actually burn more fat, sacrifice less muscle and get a better anabolic effect than regular steady state exercise/cardio. Plus more efficient as gets better results in less time. Hope this helps.