Diarrhea: A familiar phenomenon with unusually frequent or unusually liquid bowel movements, excessive watery evacuations of fecal material. The opposite of constipation. The word "diarrhea" with its odd spelling is a near steal from the Greek "diarrhoia" meaning "a flowing through." Plato and Aristotle may have had diarrhoia while today we have diarrhea. There are myriad infectious and noninfectious causes of diarrhea.

Persistent diarrhea is both uncomfortable and dangerous to the health, as it can indicate an underlying infection. It may also mean that the body is not able to absorb some nutrients due to a problem in the bowels. Treatment includes drinking plenty of fluids to prevent dehydration, over-the-counter remedies in most cases, and medical examination if diarrhea persists for more than a couple of days, particularly in small children or elderly people.