About solid state materials

Solid-state materials can be classified into three groups:
                 1. insulators
                 2. semi conductors
                 3. conductors

Insulators :
Insulators are those materials that don't conduct electricity under normal conditions. For instance: air is an insulator. You don't get electrocuted when approaching a plug point since air is an insulator. 
. The outer most orbit of an atom can be divided into various sub orbitals or bands. As you can see I have divided into three colors. The lower most band is called a valence band. The electrons in this band determine the valency of the atom. The upper most band is called the conduction band. In this band, the electron is farthest from the positively charged nucleus and is capable of easily escaping out of the atom and thus enabling the material / atom to conduct electricity.

Single Word : zero conductivity

semiconductors :
Semiconductors are materials that behave like both conductors and insulators. In certain condition a semiconductor acts like a conductor. For example charcoal and graphite which are allotrope of Carbon act as conductor. Whereas diamond which has a different crystal structure act as an insulator. The conductivity of semiconductors can be increased by adding certain impurities to them this is called doping. The conductivity may increase by pumping energy into semiconductor crystal in the form of heat or light.

Single Word : conducts by external influence (energy,temperature) 

Conductors :
Conductors are substances that easily let electrical charge pass through them with relatively very-less resistance. Almost all metals are conductors. When ever you cut an electric wire, you can see copper or some other metal at its core. Its because these metals can easily conduct electricity. 
 there is no forbidden energy gap. The valence and conduction band are overlapping each other. Hence its extremely easy for electrons to move from valence to conduction band. Hence conductors easily conduct electricity without much loss of energy. They conduct electricity under normal conditions.

Single word :  External influence is not required to conducts.