rapid development; boom; surge
Describes a sudden, sharp growth in development, sales, popularity, or other measurable expansion. Often used in business, technology, and economic contexts.
The IT industry has undergone rapid development in this region.
Sales of the new product boomed, bringing record profits.
発展 means development or expansion in general, without the 'sudden' nuance. 急発展 adds the sense of rapidity or a boom.
Compound of 急 (kyū, 'sudden, rapid') and 発展 (hatten, 'development, expansion'). The reading follows standard on'yomi.