noun
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.
この地域ではIT産業が急発展を遂げた。
The IT industry has undergone rapid development in this region.
新製品の売り上げが急発展し、記録的な利益を上げた。
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.