A Logic Gate
is an array of components arranged inside an IC (integrated circuit) that perform some sort of Boolean logic
function. Typical logic gates include an AND, OR, or NOT gate. These compare the digital voltages of their input pin(s) and output a value that corresponds to how the gate functions.
For example, let's say you have a TTL compatible AND gate that had both its inputs set to a value of 1 (a voltage equivalent to 2.2v or higher). Assuming we had positive logic (high voltage = 1, low voltage = 0) then the output of the AND gate would produce a high voltage (output = 1). If you removed the voltage off of one of the input pins, the output would reflect the change and output a 0 (low voltage = 0). The data arranged from each gate can be arranged in what is called a truth table. Truth tables are a way of visually displaying logic functionality in a concise fashion. Other logic gates can include NAND, NOR, XOR, and XNOR functions as well.