When it comes to bowel function and elimination some people's bodies are so precise they could stand in for the atomic clocks at NASA. For others bowel movements are so infrequent that each one is cause for celebration. Diarrhea and constipation are opposite extremes of bowel dysfunction. Both are unpleasant and uncomfortable and both offer important clinical insights. Occasional irregularity is not cause for immediate alarm but chronic severe issues are signs not only of potential digestive distress but also offer clues to dysfunction elsewhere in the body.
Diarrhea usually refers not just to going too frequently and with urgency but also to stool consistency being loose and liquid. Since loose runny urgent stools are the body's way of quickly getting rid of something toxic (e.g. a foodborne pathogen) or something it can't digest well (like wheat or dairy) chronic diarrhea can be considered less a problem of pathology in the bowel than simply the result of dietary factors discordant with an individual patient's physiological tolerance.