Meaning of “subway” - Learner’s Dictionary

subway

noun [ C ] uk us /ˈsʌbweɪ/
PASSAGE UK (also UK/US underpass)

B2 a passage under a road or railway for people to walk through

TRAIN US (UK underground)

a system of trains that travel underground:

We can take the subway to Grand Central Station.

(Definition of “subway” from the Cambridge Learner’s Dictionary © Cambridge University Press)