Irritable bowel syndrome (IBS) is a gastrointestinal disorder characterized by the presence of a cluster of symptoms and signs in adult or children that include cramping, abdominal pain, increased gas, altered bowel habits, food intolerance, and bloating (distention).rritable bowel syndrome (IBS) is a gastrointestinal disorder characterized by the presence of a cluster of symptoms and signs in adult or children that include cramping, abdominal pain, increased gas, altered bowel habits, food intolerance, and bloating (distention).