Gastroenteritis, or stomach flu, is an inflammation of the gastrointestinal tract that causes symptoms like diarrhea, vomiting, abdominal cramps, and sometimes fever. It is most commonly caused by viral infections such as norovirus or rotavirus, but bacteria like E. coli and Salmonella, as well as parasites and toxins, can also be responsible. Symptoms typically appear within one to three days of exposure and can last up to a week, with dehydration being a key concern, especially for children, older adults, and immunocompromised individuals. Treatment focuses on rehydration through fluids and electrolytes, while antibiotics are reserved for bacterial cases. Prevention relies on good hygiene, proper food handling, and avoiding contaminated sources to reduce infection risk.