An OR gate can have two or more inputs. The output of an OR gate is true when at least one of its inputs is true.
Galvanometer A very sensitive meter used to measure tiny currents, usually 1mA or less.
Relay An electrically operated switch, for example a 9V battery circuit connected to the coil can switch an AC mains circuit. The rectangle represents the coil. NO = Normally Open, COM = Common, NC = Normally Closed.
Thermistor A transducer which converts temperature (heat) to resistance (an electrical property).