The term "humours" comes from the Latin word "humor", which means "fluid" or "liquid." In ancient and medieval medicine, it was believed that the human body contained four primary fluids or "humours": blood, phlegm, yellow bile, and black bile.
These fluids were thought to influence both physical health and personality. The balance or imbalance of these humours was believed to determine a person's temperament and susceptibility to disease.
They are called "humours" because they were considered the essential bodily fluids responsible for health and disease. The concept was central to ancient Greek and Roman medicine, especially as described by Hippocrates and Galen.