Nor[, , ... ] is the logical NOR function. It evaluates its arguments in order, giving False immediately if any of them are True, and True if they are all False.
Nor[, , ... ] can be input in StandardForm and InputForm as ... . The character can be entered as nor or \[Nor].
Nor[, , ... ] is equivalent to Not[Or[, , ... ]].
Nor evaluates its arguments in a non-standard way (see Section A.4.2).
Nor gives symbolic results when necessary, removing initial arguments that are False.
Nor is not Flat.
See The Mathematica Book: Section 1.5.6.
See also: LogicalExpand, Or, Xor.