Take your pick from http://www.acronymfinder.com/ when in doubt.
Good resource, Vikingo!
Is this a crime or legal-type series?
OP stands for "Order of Protection" in some states' courts.
So what is an Order of Protection? Is that when the police sit outside someone's hospital room, outside their house, etc. because they think the person is under a death threat or is is similar to a TRO commonly used in TV series (Temporary Restraining Order)?
Yes, they have different names in different places.
They are a misnomer. How does a piece of paper protect somebody? It is just an order from a judge saying that if the respondent commits a crime of violence against the petitioner, that it will be an extra crime for doing it against the judge's orders. Like that's going to stop someone if they are going to do it in the first place.
There are, however, No Contact OP's. They make it a crime for the respondent to have any contact or attempted contact whatsoever with the petitioner. A good thing if the person respects the law and you want him/her out of your life, but still not going to keep them from attacking if they're set on doing it.
There was a lady murdered in our state last week that had an OP in place against her killer. Again, the police cannot do anything until the respondent breaks the law, and many times by then, it's too late.