If you can get a hold of the latest issue of TBM, there is a great article on back tension. For me it is hard to describe.

When I taught my son what back tension is, I had him put his hand on my back (right between the shoulder blades) when I drew, got to full draw and released, I could see a lightbulb go off in his head.

When I think of it, I picturepinching and holdinga silver dollar between my shoulder blades.

It's what keeps the string back at full draw and does not allow you to let the string forward before releasing and allows for a crisp release. It also isneeded to get good alignment with the target, tip of the arrow, nock, and back of draw elbow. I can get to full draw and anchor without back tension, but to get in proper alignment, I have to use it.