Patented Drugs :
Pharma companies do years of research to formulate drugs for a specific disease. They file for a patent for the drug they produce. A patented drug cannot be manufactured by another company. This way the company that had done the research to find a cure for the disese can sell the drug for a fixed period of time to recover the money they spent on research and also make profits.
Generally the patent period will be around 20 years.
Once this 20 year patent period of the drug expired any company can manufacture the drugs and sell them. So the drugs produced this way after the patent has elapsed are called Generic drugs.