A tricky little knot that works great when suspending a bead as a pendant, because it doesn't skew the cords as a doubled overhand knot does. Looks like a little "X".

Lydia Chen shows a different method in her book on Chinese knotting, which is where I first found it - she calls it the Double Connection Knot, if I remember correctly.

I've never tried the method shown in the link (frankly, it gives me a brain cramp) as Lydia's method works just fine when it comes to tightening the knot exactly where you want it.