What condition is described by a constant urge to pass stool without relief?

The condition characterized by a constant urge to pass stool without relief is tenesmus. This symptom typically occurs due to inflammation or irritation in the rectum or lower gastrointestinal tract. Patients may feel as though they need to have a bowel movement, but they are unable to produce significant stool or feel incomplete after having a bowel movement. This sensation can result from various conditions, including infections, inflammatory bowel disease, or rectal dysfunction.

In contrast, constipation refers to infrequent or difficult bowel movements, while diarrhea involves increased frequency and liquidity of stools. Irritable bowel syndrome can present a range of symptoms, including abdominal pain, bloating, and varying bowel habits, but does not specifically describe the constant urge without relief. Thus, tenesmus is accurately identified as the condition best described in the question.