Gastroenteritis involves diarrhea or vomiting, with noninflammatory infection of the upper small bowel, or inflammatory infection of the colon, both part of the gastrointestinal tract.
Usually this is caused by an infection, but this is not always the case. It usually is of acute onset, normally lasting less than 10 days and self-limiting. Sometimes it is referred to simply as 'gastro'. It is often called the stomach flu or gastric flu even though it is not related to influenza.
If the inflammation is limited to the stomach, the term gastritis is used, and if the small bowel alone is affected it is enteritis.