noun
A very large, heavily populated urban complex, often formed by the merging of several cities. Used in geography and urban studies.
東京から大阪にかけての地域は、世界有数のメガロポリスだ。
The area from Tokyo to Osaka is one of the world's leading megalopolises.
A more general Japanese term for a huge city, not necessarily a continuous urban chain.
From English 'megalopolis', ultimately from Greek 'megas' (great) + 'polis' (city).