A resistor is a component used in a circuit to control the flow of electrons. A resistor gives resistance, which is measured in ohms.

Resistors can be made from various materials depending on the application, but common types include carbon composition, carbon film, metal film, metal oxide film, and wirewound resistors, using materials like carbon, metal alloys, or metal oxides. 

There are two basic types of resistors: linear and non-linear.

Linear resistor-

A "linear resistor" is a type of resistor where the resistance value remains constant regardless of the applied voltage or current, meaning its current-voltage relationship is a straight line. 

Non-linear resistor-

Non-linear resistors are components where resistance changes with factors like voltage, current, temperature, or light, unlike linear resistors that follow Ohm's Law. Examples include thermistors, varistors, and light-dependent resistors (LDRs).