Terry v. Ohio- What is a Terry Stop?

In the landmark case, Terry v. Ohio, the Supreme Court ruled that a police officer may stop someone if there is reasonable suspicion to believe that a crime is afoot. This means that an officer does not need a warrant or even probable cause to detain someone.  However, the officer is only allowed a reasonable amount of time to either confirm or deny their suspicions about the crime.

So what is the difference between probable cause and reasonable suspicion?
Reasonable suspicion is a lower bar than probable cause. The officer has to be able to articulate sufficient facts to believe that a crime is occurring or recently occurred.  Although the officer would have to give a reason as to their suspicion, it could simply be something to the effect of, "he was in the general area of the crime and walked away when I approached him."  
On the other hand, probable cause requires the officer to have sufficiently trustworthy facts to stop the person.  In this instance, if the police officer sees you run a red light, then it is sufficient enough to pull you over and give you a citation. Seeing someone running the red light is sufficiently trustworthy.

To sum it up, a terry stop is the ability of an officer to stop a person and ask them questions.  It is perfectly legal as long as there is reasonable suspicion and the length is reasonable as well.