Low ready is a handgun shooting stance and grip which means you've got both hands holding your loaded firearm*, safety off (with finger OFF the trigger of course), pointing it just slightly below your intended point of impact on your target (to allow you to more clearly see what your target is up to), and your head slightly lowered to allow you to acquire a good sight picture.

This is used when holding somebody at gunpoint (like when apprehending a potentially armed suspect) or when moving through a course of fire in training or in real combat.

To see a perfect example of an operator holding a pistol at low ready look at the cover of the Red Storm game Rainbow Six.

The person featured on that picture is not really a spec ops team member but is actually John T. Meyer, Jr., Vice President of Sales at Heckler & Koch USA. The gun used was a H&K USP 40.

To learn more about the origins of that picture (and all things H&K) go to http://www.hkpro.com/r6usp.htm

Pretty cool huh?

* "Loaded" means that there is a round in the chamber, not just a loaded magazine.