Obsessive compulsive disorder (OCD) is a mental health disorder that affects people of all ages  and walks of life, and occurs when a person gets caught in a cycle of obsessions and compulsions . Obsessions are unwanted, intrusive thoughts, images, or urges that trigger intensely distressing feelings. Compulsions are behaviors an individual engages in to attempt to get rid of the obsessions and/or decrease distress.
Most people have obsessive thoughts and/or compulsive behaviors at some point in their lives, but that does not mean that we all have “some OCD.” In order for a diagnosis of OCD to be made, this cycle of obsessions and compulsions must be so extreme that it consumes a lot of time (more than an hour every day), causes intense distress, or gets in the way of important activities that the person values.
What exactly are obsessions and compulsions?
Obsessions are thoughts, images, or impulses that occur over and over again and feel outside of the person’s control. Individuals with OCD do not want to have these thoughts and find them disturbing. In most cases, people with OCD realize that these thoughts are illogical.
Obsessions are typically accompanied by intense and uncomfortable feelings such as fear, disgust, uncertainty and doubt, or a feeling that things have to be done in a way that is “just right.” In the context of OCD, obsessions are time-consuming and get in the way of important activities the person values. This last part is extremely important to keep in mind as it, in part, determines whether someone has OCD — a psychological disorder — rather than an obsessive personality trait.
How is this different from being "obsessed"?
“Obsessing” or “being obsessed” are commonly used terms in everyday language. These more casual uses of the word mean that someone is preoccupied with a topic, an idea, or even a person. To be “obsessed” in this everyday sense doesn’t mean that a person has problems in their day-to-day living — there may even be a pleasurable component to their experience of being “obsessed.” For example, you can be “obsessed” with a new song you hear on the radio, but you can still meet your friend for dinner, get ready for bed in a timely way, get to work on time in the morning, etc., despite this obsession.
The content of an everyday “obsession” can be more serious: for example, everyone might have had a thought from time to time about getting sick, or worrying about a loved one’s safety, or wondering if a mistake they made might be catastrophic in some way. While these thoughts look similar to what you would see in OCD, someone without OCD may have these thoughts, be momentarily concerned, and then move on.
In fact, research has shown that most people have unwanted intrusive thoughts from time to time, but in the context of OCD, these intrusive thoughts come frequently and trigger extreme anxiety that gets in the way of day-to-day functioning.
Common Obsessions in OCD 
Religious/Moral Obsessions (Scrupulosity)
Compulsions are repetitive behaviors or thoughts that a person uses with the intention of neutralizing, counteracting, or making their obsessions go away. People with OCD realize this is only a temporary solution, but without a better way to cope, they rely on compulsions nonetheless. Compulsions can also include avoiding situations that trigger obsessions. They are time-consuming and get in the way of important activities the person values.
Compulsions vs. Rituals
Similar to obsessions, not all repetitive behaviors or “rituals” are compulsions. This depends on the function and the context of the behavior. For example, bedtime routines, religious practices, and learning a new skill all involve some level of repeating an activity over and over again, but are usually a positive and functional part of daily life. Similarly, arranging and ordering books for eight hours a day isn’t a compulsion if the person works in a library.
The feelings associated with a behavior also indicate whether it is compulsive. If you are just a stickler for details or like to have things neatly arranged, you might consider these things to be “compulsive” behaviors, but that doesn’t necessarily mean they are symptoms of OCD. In these cases, “compulsive” refers to a personality trait or something about yourself that you actually prefer or like. In most cases, individuals with OCD feel driven to engage in compulsive behavior and would rather not have to do these time-consuming and often torturous acts. Rather than being a source of pleasure, people with OCD perform compulsions because they believe these rituals are necessary to prevent negative consequences and/or to escape or reduce anxiety or the presence of obsessions.
Common Compulsions in OCD 
Washing and Cleaning
-  National Institute of Mental Health. (n.d.) Obsessive-Compulsive Disorder. NIMH Information Resource Center. https://www.nimh.nih.gov/health/statistics/obsessive-compulsive-disorder-ocd ↩
-  American Psychiatric Association (2013). Diagnostic and statistical manual of mental disorders. 5th ed. Washington, DC: American Psychiatric Association. ↩
-  Clark, David A. & Radomsky, Adam S. (2014). Introduction: A global perspective on unwanted intrusive thoughts. Journal of Obsessive-Compulsive and Related Disorders. Available online 18 February 2014. DOI: 10.1016/j.jocrd.2014.02.001 http://www.sciencedirect.com/science/article/pii/S2211364914000128 ↩
-  Reprinted with permission by New Harbinger Publications, Inc. This is an adaptation of the OC Checklist which appears in S. Wilhelm & G. S. Steketee's Cognitive Therapy for Obsessive-Compulsive Disorder A Guide for Professionals (2006). www.newharbinger.com ↩