A circuit that outputs high (1) only when all inputs are low (0) is known as what?

The circuit described in the question outputs high (1) only when all inputs are low (0), which corresponds to the behavior of a NAND gate. A NAND gate produces a low (0) output only when all its inputs are high (1). In every other situation—when at least one input is low—the output will be high (1). Therefore, when all inputs are low (0), the NAND gate's output is high (1), matching the description provided.

This behavior distinguishes the NAND gate from other types of logical gates. An AND gate, for example, would require all inputs to be high (1) to output high (1). An OR gate produces a high (1) output if any of its inputs are high (1). Lastly, an XOR gate generates a high (1) output when the number of high (1) inputs is odd, which does not align with the requirement that all inputs must be low for the output to be high. Thus, the NAND gate is the appropriate answer.