Why is bowel movement called stool?

The term "stool" is used to refer to bowel movements because it is a solid waste product that is produced by the digestive system and eliminated from the body through the rectum. The word "stool" is derived from the Old English word "stol," which means "a seat or chair," and was originally used to describe a raised seat used for sitting on. Over time, the term came to be used figuratively to refer to anything that is solid and immovable, and eventually came to be applied to bowel movements due to their solid form and the fact that they are eliminated from the body in a sitting position.