What is rumination?

I see so many people talking about "rumination." I always understood OCD as just obsessions and compulsions and thought if I just don't give into the compulsions, then the obsessions go away. For instance, I feel the urge to delete some account that I feel is "contaminated" in some way. I haven't for like a month, but the obsession is still there. I think I may be "ruminating" or dwelling on it too much...how do I stop this?

Rumination is the focused attention on the symptoms of one's distress, and on its possible causes and consequences, as opposed to its solutions. It is one type of compulsion.
Congratulations for not deleting the account for a month. Continue for one more month without deleting and you will hopefully get tired of dwelling on it and stop.

A good answer by helloagain. Regarding how to deal with rumination, I find the best bet is usually to distract yourself. If you find yourself ruminating, suddenly switch up what you're doing to something new; preferably something that requires your focus like a video game or certain chores.