三焦是中医学范畴中六腑之一，又名「决渎之官」，为上焦、中焦、下焦三者的统称；对应的脏为心包。「焦」古作「膲」，为皮下、肌间纹理之意。过去英文意译成「Three warmer」、「Triple warmer」、「Triple burner」，理由是与身体代谢有关。

根据《素问·灵兰秘典》：「三焦者、决渎之官、水道出焉。」遍布在人体胸腔及腹腔，是血气、津液运行至五脏六腑的途径，故此，三焦与其他腑器不同，并无实体，明确位置亦有不同的说法及见解；亦有认为三焦对应解剖学的内分泌系统。然而，三焦与个别脏腑之间的关系极为密切，可以用来调整及辅助脏腑的机能，所以三焦亦可说是脏腑的「外府」与「外卫」。

San Jiao is a term found in traditional Chinese medicine (TCM), as part of the modelling of the workings of the human body attempted by early Chinese medical writers. References to it can be found in the oldest Chinese medical texts available, including the Yellow Emperor's Huang Di Nei Jing.The identification of disease according to the Three Burners (三 焦) was first described in the Qing Dynasty (1644-1911) by Wu Ju Tong (吳鞠通, 1758–1836) in his book A Systematic Identification of Febrile Diseases.. This system is used within the practice of Chinese herbal medicine, in conjunction with acupuncture and other Chinese medicine (TCM) modalities. Note that the San Jiao theory differs slightly from the San Jiao organ, or channel [(Shou Shao Yang, san jiao jing)]; referred to additionally as "Triple Heater", San Jiao, and "Triple Burner". Viewed by Chinese Medicine as the passage of heat and fluid throughout the body, Elementary Questions (su wen)' explains, "The Triple Burner holds the office of the sluices; it manifests as the waterways."