A NOR gate is a combination of an inverter and an OR gate. Its name derives from its NOT-OR function. Like the NAND gate, the NOR gate can also be used to construct an AND gate, an OR gate, and an inverter.
the bellow the truth table for a two- input NOR gate. Notice that the output is the complement of the OR-function output. A 1 occurs only when
0 is applied to both inputs. A 1 input produces a 0 output.