False imprisonment is the act of holding a person against their will and not allowing them to leave a particular place by restraining them. However, this does not typically include law enforcement provided that they are following the law. In this sense, a police officer would not be liable for false imprisonment of a suspect, as it would be within their power to stop a suspect from fleeing without the use of restraints.
A person does not have to be tied up for it to be considered false imprisonment; they simply have to be restrained from exercising their free will to leave.
False imprisonment is a serious crime and considered a felony that could warrant several years of incarceration. The term is used when an adult is held against their will as opposed to kidnapping (when it is a child).