Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder that primarily affects the large intestine (colon). It is a common condition, characterized by a combination of symptoms that can vary in severity and duration. The exact cause of IBS is not known, but it is believed to involve a combination of factors, including abnormal muscle contractions in the intestine, changes in the gut's sensitivity to certain stimuli, and disturbances in the gut-brain communication.