Copper, aluminium, silver is some common examples of conductors. We may define conductor as given below.
1. A material is said to be a conductor if it permit electricity or current through it freely or more simply.
2. A material is described as a conductor if the width of the forbidden band in energy band structure is zero, that means there is overlap in conductor and valence bands.
Figure: Conductors Energy Band Structure
3. A medium is described as conductor if σ/ ωε is very high. Here σ is conductivity, ε is permittivity and ω is angular frequency,.