Nand[e1, e2, ...] is the logical NAND function. It evaluates its arguments in order, giving True immediately if any of them are False, and False if they are all True.
Nand[e1, e2, ...] is equivalent to Not[And[e1, e2, ...]]. »
Nand has attribute HoldAll, and explicitly controls the evaluation of its arguments. In Nand[e1, e2, ...] the are evaluated in order, stopping if any of them is found to be False. »
Nand gives symbolic results when necessary, removing initial arguments that are True. »