Urea is a compound used as fertilizer that is composed of four letters. It is an organic compound that is a colorless, odorless solid, highly soluble in water, and practically non-toxic. Urea is produced commercially from ammonia and carbon dioxide and is the main nitrogen-containing substance in the urine of mammals. It is also used in many industrial processes, such as the production of plastics and pharmaceuticals. In agriculture, urea is used as a fertilizer to provide plants with the nitrogen they need for growth.