Obsessive-compulsive disorder (OCD) is represented by a diverse group of symptoms that include intrusive thoughts, rituals, preoccupations, and compulsions. A person with OCD may have an obsession, a compulsion, or both. An obsession is a recurrent and intrusive thought, feeling, idea, or sensation whereas a compulsion is a behaviour which is conscious, standardized, recurrent, such as counting, checking, or avoiding. A person with OCD realizes the irrationality of the obsession and experiences both the obsession and the compulsion as unwanted behaviour.