Diode A device which allows current to flow in only one direction.
Light Emitting Diode A transducer which converts electrical energy to light. Usually abbreviated to LED.
An AND gate can have two or more inputs. The output of an AND gate is true when all its inputs are true.
Preset variable resistor A preset is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than standard variable resistors so they are sometimes used in projects to reduce the cost.