What is OCD?

I'll start out simply by answering the question, what is OCD? Obsessive Compulsive Disorder is a mental illness characterised by, get this, obsessions and compulsions. Obsessions are recurring, sometimes constant, intrusive thoughts that cause the individual distress and extreme anxiety. These can come in the form of images or impulses the individual finds disturbing. Usually when a person has a random, unprovoked disturbing thought they can dismiss it. However, in people with OCD the illness causes that to be exceedingly difficult, and thus their minds obsess over them, causing it to be nearly impossible to think of anything else. This leads to constant worry, severe anxiety and compulsions.
Compulsions are actions one takes to avoid the obsession or the prospect of the disturbing thought coming true. For example, one could have the thought that touching something would result in them contracting an illness thus the compulsion would be washing their hands. The catch is, compulsions only relieve the anxiety for a short time before the obsession starts again. "Well you didn't wash them well enough." or "Maybe you accidentally touched something else since then without realising."
The individual IS AWARE that these obsessions are often irrational sometimes flat out impossible but that does not lessen the illness's ability to cause severe anxiety. Knowing that what's causing you anxiety is irrational is extremely frustrating but OCD preys on the irrational part of the mind leaving the person warring within their brain. I used the hand washing example because many people attribute obsessive cleanliness to OCD. However this is not always the case. Obsessions and compulsions come in many forms taking shape as whatever the individual finds most disturbing at the time. They could have images in their mind of hurting a loved one, something they would NEVER DO or willingly think of and they find it so distasteful that the very thought causes panic. As you can imagine, thoughts like that often cause a downward spiral of self hatred, confusion, and terror. Many with OCD are so consumed with worry they find daily life difficult, even impossible.