The Nikon DX system is Nikon’s name for the APS-C sensor size (24x16mm) DSLR system. Nikon uses this sensor size in their consumer-level DSLR cameras. The brand has a special series of DX lenses which have a smaller image projection area to cover the smaller sensor.
The Nikon DX mount is physically identical to the standard F mount, but the smaller image circle of the lenses leads to heavy vignetting. Accessories made for Nikon F DSLR cameras are compatible with Nikon DX cameras.