A NOT gate can only have one input. The o on the output means not. The output of a NOT gate is the inverse (opposite) of its input, so the output is true when the input is false. A NOT gate is also called an inverter.
A NOR gate can have two or more inputs. The o on the output means not showing that it is a Not OR gate. The output of a NOR gate is true when none of its inputs are true.
Thermistor A transducer which converts temperature (heat) to resistance (an electrical property).
Amplifier (general symbol) An amplifier circuit with one input. Really this is a block diagram symbol because it represents a circuit rather than just one component.