This is a knot that makes two loops which can be tightened down around someone's two wrists. While it can be convenient for capture, great care must be taken because of the ease with which the loops will continue to tighten, and the tendency for a single loop of rope around the wrists to dig into vulnerable nerves in the wrist groove. Generally, I view this technique as to be avoided.

I've seen two versions of this tie, one which uses simple loops and the other a prusik. The principle is the same; the knot is meant to provide enough friction that the cuffs won't easily tighten or loosen except when being pulled directly through the knot, much like a Taut Line Hitch.