what is d3d usage?

This is the amount of memory used by the GPU via DirectX/Direct3D. It doesn't cover memory usage via other interfaces (like OpenCL for example).
Unfortunately, AMD doesn't seem to offer an universal way how to report exact memory usage of the GPU (like nVidia), so this is currently the only way how to get a picture of memory usage.
I see:

GPU Utilization
GPU D3D Usage
GPU D3D Memory Dedicated
GPU D3D Memory Dynamic

I thought GPU D3D Memory Dedicated showed the memory used by the GPU. Dynamic showed the memory for the graphics card (gpu and memory) that is in the system memory.

GPU D3D Usage is definitely not showing the amount of memory used by the GPU.
Ah, sorry - "GPU D3D Usage" should display GPU utilization via Direct3D and "GPU D3D Memory" the GPU memory utilization.
Theoretically they should be close.
"GPU Utilization" is read straight from the GPU internal registers, so this should be the more precise value and it should cover the entire GPU.
"D3D Usage" is read via Direct3D, so it covers only this interface.
Unfortunately, hardware vendors don't give out information that would help us to understand such things, so sometimes we're just left to try and see...
Hey Guys my name is Mark.Well i think that D3D is used to provide three perspective design in programs where performance is essential, such as activities. D3D also allows programs to run fullscreen instead of included in a screen.Thanks!!

Double Ended Beam Load Cells
Martin said:
"D3D Usage" is read via Direct3D, so it covers only this interface.

AMD A10-6800K

I set CPU 4000 MHz / GPU 800 MHz (in idle they fall to 2000 / 300)

Windows 7 SP1 (default aero theme)
HWiNFO x64

In idle I see 20-60% Utilization and 0-3% D3D Usage.

In max load I see 99% Utilization and 100% D3D Usage. No matter - D3D or OpenGL!

Furmark - OpenGL - 100% D3D Usage.

After runing OpenGL Extension Viewer 4.1.3 test:
Utilization (max): 94.0%
D3D Usage (max): 96.9%
Thanks for the results, it's interesting. So it seems the D3D Usage covers OGL as well.