Not OR.

The boolean function which is true if none of its inputs are true and false otherwise, the logical complement of inclusive or. The binary (two-input) NOR function can be defined (written as an infix operator):

A NOR B = NOT (A OR B) = (NOT A) AND (NOT B)

Its truth table is:

        A | B | A NOR B
        --+---+---------
        F | F |    T
        F | T |           F
        T | F |    F
        T | T |    F

NOR, like nand, forms a complete set of boolean functions on its own since it can be used to make NOT, AND, OR and any other Boolean function:

NOT A = A NOR A

A OR B = NOT (A NOR B)

A AND B = (NOT A) NOR (NOT B)