détendeur second étage
/detɑ̃dˈœʁ pʁəmjˈeʁ etˈaʒ/
n
English: regulator second stage · 二级减压器
Sens：Apparatus that changes the pressure of the air coming from the regulator first stage to the pressure of the ambient air; the diver breathes this air in through a mouthpiece.