The resistance which can be changed as desired is called variable resistance.
Apart from varying currents, this element is also used to control some basic parameters like speed, temperature for commonly used electrical loads.
As the resistance is varied, the current in the load varies as per Ohms Law.
The symbol for a variable resistor is shown below.
A fixed resistance is called a resistor because we can't change the value of a resistor according to our needs.
A fixed resistance implies that the resistance of the device remains constant and cannot be changed.
Fixed resistances are used particularly to control and limit the current in a known circuit and to produce a specific amount of heat every time through the application of the heating effect of electric current.
An insulator is a material that does not conduct an electrical current.
The atoms of the insulator have tightly bound electrons which cannot readily move.
Insulators have higher resistivity than semiconductors or conductors.
Examples of insulators include plastics, paper, rubber, glass, and dry air.
A conductor is an object or type of material that allows the flow of charge in one or more directions.
Materials made of metal are common electrical conductors.