A non-dim circuit is a special electrical network.
The word non-dim is used to distinguish this type of circuit which operates only in on or off modes, from a dimmer, which can be at any intensity on a continuum.
Many modern computerized lighting systems allow a dimmer to be set as "non-dim" and controlled using the Lighting control console, however, this can be less desirable than using a "true" switched circuit, as the Triac in the dimmer never truly supplies a "proper" sine wave, which can cause damage to equipment.
Non-Dims are often used to allow switched equipment such as motors, hazers or other similar electrical equipment to be triggered as part of a lighting cue.
It is also sometimes used to provide power to intelligent lights, however this may not be considered desirable as any mistakes made at the Lighting control console could interrupt the power supply to the fixture which often are not capable of hot restrike (turning on the lamp again while power is still connected) due to their use of a Metal halide lamp or similar lamp.