That may have been the terminology in your police days, but today, "detention" is quite different than "arrest". Detaining someone only requires an officer to have "reasonable suspicion", while arresting someone requires "probable cause". Making an arrest without probable cause can be a quick way to the unemployment line.
Originally Posted by David Goldstein
An arrest also gives an officer the authority to conduct a complete search of the individual, as well as the person's vehicle, and it gives the officer the authority to remove the person from the scene. Detention simply allows the officer to keep the individual from leaving, for a short period of time, while they investigate and question the individual.
Bottom line, if a currently employed officer believes that "arrest" and "detain" are legally classified as the same thing, he/she is in the wrong line of work.