What's the main difference between FX & DX format Nikkor Lenses?

What's the main difference between FX & DX format Nikkor Lenses?

The amount of coverage. The DX lenses throw a smaller image circle. They are designed to cover the smaller DX sensor. FX lenses throw a "full size" image circle and are suited for full format sensors, but will work perfectly well on DX sensors, too.

Everything above, and:

DX lenses are cheaper than an FX lens, because the glass elements can be made smaller. The DX lens only needs to project a 24mm circle to the sensor, not the 36mm of a full frame FX.

You can use DX lenses on FX digital bodies. The camera detects the DX lens and crops down. Not an ideal solution, the 12MP camera turns into a 6MP camera.