Correct
三伏
/ sānfú /
Strokes
Definition
three periods forming the hottest periods of summer, from mid-July to mid-August, namely: 初伏 (mid-July), 中伏 (late July to early August), 末伏 (mid-August)
Example
As a Noun
three fu ［three hottest ten-day periods of the hot season］
As a Noun
third fu ［third ten-day period of the hot season］