Let me help all the Billy badasses in here
Detained requires a lower burden of proof than an arrest (reasonable suspicious vs probable cause). A traffic stop is an example of a detention, in which the officer has a reasonable suspicion that a crime (or infraction) will, has been, or is about to be committed. This detention allows the officer to investigate his/her reasonable suspicion to see if it turns into probable cause or is nothing.
In a detention, you are not free to leave but you are not under arrest. In a detention, you can (and probably will) be restrained temporarily (for everyone's safety) until they investigate information provided by yourself and others and determine you do not pose an extreme risk by being unrestrained.
The easiest way to remember this:
A detention is made when an officer has a reasonable suspicion that you are about to, in the process of, or recently committed a crime.
An arrest is made when an officer believes a crime was committed and you probably did it.
Don't quote me, I'm not a lawyer and have never played one on TV. Just some guy on the internet.