'Sān fú' (the 'three dog days') refers to the hottest, most humid 30- or 40-day period in traditional Chinese solar terms, occurring roughly from mid-July to mid-August. The term combines 三 (sān, 'three') and 伏 (fú, literally 'to crouch' or 'to hide'), symbolizing how heat forces people and animals to seek shelter—hence the folk name 'dog days,' evoking dogs panting in the sweltering sun. It is divided into 'early fu' (chū fú), 'mid fu' (zhōng fú), and 'late fu' (mò fú), each lasting about ten days, determined by the lunar calendar and the summer solstice.

This concept originates from ancient Chinese cosmology and medicine: it's believed that the body’s yang energy peaks during sān fú, making it an ideal time for 'fu tie' (herbal patches applied to acupoints) and dietary therapy like eating dumplings or noodles to strengthen qi. While not a formal holiday, sān fú is widely referenced in weather reports, health advice, and regional customs across China.