Having worn one for 6 years prior starting my driving career, would you mind if I told you that both terms are incorrect? In a uniform configuration, it is a duty belt. A duty belt, worn over a uniform blouse or jacket, with a shoulder strap for support, is a Sam Brown rig. A duty belt, attached with keepers or hook-and-loop, to a garrison belt which is looped through the belt loops on your trousers, is a Garrison rig.
Without the shoulder strap or garrison, it really is just a belt.