It’s a sort of subway/general railway hybrid that runs between downtown Manhattan and New Jersey (Newark and Hoboken). “PATH” is the ugly name thought up by the Port Authority of New York, who took it over when the original private operator went bankrupt; stands for “Port Authority Trans-Hudson” (Railroad). Original name was Hudson & Manhattan Railroad. It was the first railroad that tunneled under the Hudson River; started running in 1907.
Thanks to all who replied. Learn something new everyday.