‘疯长’ literally combines ‘疯’ (fēng, meaning 'crazy' or 'wild') and ‘长’ (zhǎng, meaning 'to grow'). Together, it describes rapid, unchecked, often excessive growth — like weeds overtaking a garden or algae blooming in a pond. It carries a slightly negative or vividly emphatic connotation, suggesting growth that is hard to control, manage, or predict.

This term is most commonly used for plants, fungi, bacteria, or populations (e.g., insects or microbes), especially in ecological, agricultural, or everyday descriptive contexts. While occasionally applied metaphorically to abstract things like rumors or prices, its core usage centers on biological or physical expansion that feels overwhelming or unnatural in speed and scale. It’s informal but widely understood in both spoken and written Chinese.