LDR A transducer which converts brightness (light) to resistance (an electrical property). LDR = Light Dependent Resistor
Transistor NPN A transistor amplifies current and can be used with other components to make an amplifier or switching circuit. This symbol is for a bipolar junction transistor (BJT), the type you are most likely to use at first.
This type of variable capacitor is designed to be set when a circuit is made and then left without further adjustment.
Galvanometer A very sensitive meter used to measure tiny currents, usually 1mA or less.