1) Most often when Indian business executives  use the term metro  they refer to the mega cities in India. Historically Delhi, Mumbai (formerly Bombay) , Kolkata (formerly Calcutta)  & Chennai (formerly Madras) were classified as metros. Now Bangalore and  Hyderabad are also considered metros; sometimes Pune and Ahmedabad are included in the listing.2) Modern recent commuter train systems in Kolkata, Delhi and other cities are often referred to as the Metro. (this is the equivalent of the Underground in London, the El in Chicago, or the Subway in New York).