Direct Current (dc) - An essentially constant value current that flows in only on direction.
Duplex Receptacle - The commonly used receptacle (outlet). Called "duplex" because it has two plug-in sockets.

Fixture - Any permanently connected light or other electrical device that consumes power.
Flicker - Impression of fluctuating brightness or color, occurring when the frequency of the observed variation lies between a few hertz and the fusion frequencies of the images.
Fluctuation - A surge dip in voltage amplitude, often caused by load switching or fault clearing.
Frequency - On ac circuits, the designated number of times per second that polarity alternates from positive to negative and back again, expressed in Hertz (Hz)
Fuses - Removable devices that will heat up, melt and electrically open the circuit after a period of prolonged abnormal current flow. Link a circuit at the fuse box. Fuse connections blow apart and break the circuit if an overload or short occurs.
Fuse Arcing Time - The amount of time required of the fuse to extinguish the arc and clear the circuit; the specific amount of time required for an interrupter to clear a circuit after its fusible element has melted.