Recall that there are two ($2$) types of electricity:
- Static electricity is associated with the excess/lack of charged particles
- Current electricity is associated with the movement of charge
Conductors are materials which allow for the easy flow of electric current. Insulators do not allow this. This does not mean that insulators are undesirable when studying electricity - they are used to produce static electricity.
Electrification (a.k.a. charging) by friction is done by rubbing two unlike materials together. By the triboelectric effect, one material will lose electrons and the other gains them, becoming negatively charged in the process.
Semi-conductors
These materials are neither fully conductors nor insulators. Their conductivity is determined by their chemical makeup and the amount of voltage or light applied to them.