Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder, meaning it is a problem caused by changes in how the GI tract works. People with a functional GI disorder have frequent symptoms, but the GI tract does not become damaged. IBS is not a disease; it is a group of symptoms that occur together. The most common symptoms of irritable bowel syndrome are abdominal pain or discomfort, often reported as cramping, along with diarrhea, constipation, or both. In the past, irritable bowel syndrome was called colitis, mucous colitis, spastic colon, nervous colon, and spastic bowel. The name was changed to reflect the understanding that the disorder has both physical and mental causes and is not a product of a person's imagination.