It seems there's a few ways to spell DeSaxe but it simply means "off axis", meaning the crankshaft centreline is off axis from the centre line of the cylinder. It does a couple of things, it can be used to reduce the load on the thrust side of the piston by giving less rod angularity on the power stroke and it gives a slight assymetric timing for the exhaust and transfer ports.

Fox used it on at least some of their engines and Merco used it on all their engines (29, 35, 49 and 61). Strangely, Merco used it on the opposite side to Fox so I'd assume it's a designer choice between either reducing thrust loading or the timing assymetry. I'm sure there are other engines that may still use it today but the only one I know of is the SC 1.08 and I only found that out when I was measuring the timings and kept getting a difference between the port opening and closing degrees. I figured at first I had the degree wheel set wrong but it wasn't...