megacity; city with over a million people
Refers to a city whose population is at least one million. Often used in demographic or urban planning contexts.
Tokyo is one of the world's leading megacities.
There are three cities with over a million people in this region.
大都市 is a more general term for a large city, without specifying a population threshold.
メガシティ is a loanword often used for very large metropolitan areas, sometimes with a higher population threshold (e.g., 10 million).
Compound of 百万 (one million) and 都市 (city).