I got Tussin Maximum Strength Cough, and the active ingredients list says "Dextromethorphan HBr, USP 15mg"

What's the USP stand for? Is that something else?
zalami128 Reviewed by zalami128 on . DXM question (DXM HBr, USP?) I got Tussin Maximum Strength Cough, and the active ingredients list says "Dextromethorphan HBr, USP 15mg" What's the USP stand for? Is that something else? Rating: 5