It's just bending and manipulating the way the plant grows. The plant naturally sends hormones to the highest point of the plant height-wise. Therefore by bending the top of the plant down and below the area you want to grow, you can stimulate side growth and make it ultra-bushy. Topping + LSTing = multiple colas and nice bushy grows.
Not really a method I was aware of for our first few batches of plants...but if you look at the last page of my grow journal, you'll see a couple plants I've been LSTing for about two weeks now. Very pleased with the results.