the three annual periods of hot weather, namely 初伏[chu1 fu2], 中伏[zhong1 fu2] and 末伏[mo4 fu2], which run consecutively over a period from mid-July to late August
Definitions (Wiktionary)
noun
the third fu
noun
three fu (three periods forming the hottest periods of summer, from mid-July to mid-August, namely: 初伏 in mid-July, 中伏 in late July to early August and 末伏 in mid-August)