What is malicious prosecution? For starters, it's a personal injury cause of action, and not a crime.
Malicious prosecution is a claim that can be raised in a lawsuit. So basically, it's a reason to sue another for wrongfully prosecuting them. It's typically raised against investigators or police officers.
It's a civil lawsuit, which means that it doesn't subject the defendant to jail time. Rather, it's a lawsuit that asks for monetary damages to make the other person whole.