NAND stands for Not AND, and comprises a Not (inverter) and an AND gate in series. It is a digital integrated circuit, not to be used in analogue situations.
The states of the inputs that lead to certain outputs are displayed in the truth table:
| In A | In B | Out |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Only when all inputs are high, the output turns low.
NAND gates are considered universal gates because any other logic function can be constructed using only NAND gates.