Diarrhoea is the passage of loose or liquid stools (types 5, 6 or 7 (entirely liquid) on the Bristol Stool Chart). Severe diarrhoea is the passage of four or more loose or liquid stools daily.

Acute diarrhoea is ≤14 days, persistent diarrhoea 15–30 days, and chronic diarrhoea >30 days in duration.