Enteritis is an inflammation of the mucous membrane of the intestine — most often the small intestine. Infectious enteritis, the common form, follows contaminated food or water: viruses like norovirus and rotavirus, bacteria like Salmonella and Campylobacter, inflame the lining, which then fails to absorb properly and secretes fluid instead — producing the watery diarrhoea, cramps, nausea, and fever of gastroenteritis. The inflamed mucosa needs rest and fluids; most cases resolve as the immune system clears the invader, with oral rehydration salts replacing water and electrolytes. Severe or prolonged enteritis — Crohn’s disease, radiation enteritis — damages absorption long-term and needs specialist care. The word names the pathology behind most “stomach bugs”: not the stomach at all, but the inflamed intestine refusing to do its job.