What is meant by 'doping' in a semiconductor?

Doping is the process of adding impurities to intrinsic semiconductors to alter their properties. Trivalent and Pentavalent elements are used to dope silicon and germanium. When an intrinsic semiconductor is doped with a trivalent impurity it becomes a p-type semiconductor. When we dope intrinsic material with pentavalent impurities we get an n-type semiconductor.