The gate whose output is low if and only if all inputs are high, is
The gate whose output is low if and only if all inputs are high, is NAND.
The logic NAND gate is a combination of a digital logic AND gate and a NOT gate connected together in series.
A NAND gate (NOT-AND) is a logic gate which produces an output which is false only if all its inputs are true; thus its output is complement to that of an AND gate. A LOW (0) output results only if all the inputs to the gate are HIGH (1); if any input is LOW (0), a HIGH (1) output results.