If we are afflicted by the disease called obsessive-compulsive disorder, we will be unable to control our thoughts, obsessions, and behaviours and feel the urge to repeat them over and over again. We start doing something in response to that. For instance, you think you have mud in your hands and therefore feel dirty and keep washing them. You will feel better only after you have washed your hands countless times. But even after washing your hands many times you still feel them dirty. Or else we think we have done something wrong.
We start obsessing over our small mistakes and start worrying. Such needless thoughts can be called obsessions. The things we do in response to our thoughts can be called compulsions. Obsessions and compulsions are the symptoms of OCD. You can have various kinds of obsessions. It can be suspicions (it can be whether you have locked the door, taken a book, or switched off the cylinder), sexual thoughts, or about committing some crime. Accordingly, your compulsions will also change.
For instance, checking several times whether you have locked the door. Obsession can also mean having thoughts and feelings that are out of your character.
That can also lead to anxiety and guilt. After a point, it starts affecting your daily routine. An unusual sense of hygiene and cleaning is commonly seen in people with OCD. But obsessions and compulsions can vary among individuals. OCD is a normal mental disorder. Nowadays we see that a lot in children too, especially post Covid. There are effective treatments for this. Some of the issues can be treated through counselling. For more serious issues they need to be given medicines.