Obsessive-Compulsive Disorder, OCD, is an anxiety disorder and is characterized by recurrent, unwanted thoughts, images, or impulses (obsessions) and/or repetitive behaviors (compulsions).
Obsessions can include thoughts of germ contamination or other illness, irrational fear of having done something harmful, obsessive doubt and in turn obsessive need for certainty and constant second-guessing, amongst many other possible types of obsessions.
Repetitive behaviors such as handwashing, counting, checking, or cleaning are often performed with the hope of preventing obsessive thoughts or making them go away. Performing these so-called “rituals,” however, provides only temporary relief, and not performing them markedly increases anxiety.
Being “obsessive” can be different from having OCD, and refer to a certain personality type (perfectionism, things having to be done just-so, orderliness that falls short of being a compulsion, etc…).