Obsessive-compulsive disorder (OCD) is a psychiatric anxiety disorder most commonly characterized by a subject's obsessive, distressing, intrusive thoughts and related compulsions (tasks or "rituals") which attempt to neutralize the obsessions. The phrase "obsessive-compulsive" has worked its way into the wider English lexicon, and is often used in an offhand manner to describe someone who is meticulous or absorbed in a cause ("anal-retentive"). Such casual references should not be confused with obsessive-compulsive disorder. It is also important to distinguish OCD from other types of anxiety, including the routine tension and stress that appear throughout life. Although these signs are often present in OCD, a person who shows signs of infatuation or fixation with a subject/object, or displays traits such as perfectionism, does not necessarily have OCD, a specific and well-defined condition. Wikipedia
Mental disorder in which an individual experiences obsessions or compulsions, either singly or together. An obsession is a persistent disturbing preoccupation with an unreasonable idea or feeling (such as of being contaminated through shaking hands with someone). A compulsion is an irresistible impulse to perform an irrational act (such as repeatedly washing the hands). The two phenomena are usually, but not always, linked in the obsessive-compulsive person. Onset of the illness has been linked to malregulation of the neurotransmitter serotonin as well as to the ill effects of high stress. Encyclopędia Britannica