What is the difference in subway and metro?

The only difference is language, Americans tend call it the subway, while Brits tend to call it the underground and European countries and others tend to call it the metro. There are exceptions, with cities like Washington DC, Newcastle and Los Angeles calling their systems "Metro" and Glasgow using "Subway". Those terms are typically used to denote a rapid transit system, which is a train system that runs on its own dedicated right of way with little to no crossings with other traffic.