Definition of metro noun from the Oxford Advanced Learner's Dictionary
metro
noun
ˈmetrəʊ ˈmetroʊ
pluralmetros1(also the Metro) [singular]an underground train system, especially the one in Paristo travel on the metro / by metrothe Paris Metroa metro station2(Indian English) a large or capital city, especially Delhi, Kolkata, Mumbai or ChennaiHere are the temperatures recorded at the four metros at 5 o'clock this morning.Usage note: underground / subway / metro / tubeA city’s underground railway/railroad system is usually called the underground (often the Underground) in British English and the subway in North American English. Speakers of British English also use subway for systems in American cities and metro for systems in other European countries. The Metro is the name for the systems in Paris and Washington, D.C. London’s system is often called the Tube.
ˈmetrəʊ 
ˈmetroʊ 
Usage note: underground / subway / metro / tubeA city’s underground railway/railroad system is usually called the underground (often the Underground) in British English and the subway in North American English. Speakers of British English also use subway for systems in American cities and metro for systems in other European countries. The Metro is the name for the systems in Paris and Washington, D.C. London’s system is often called the Tube.