PRV – Set Pressure Tolerances per ASME Section I; 

Pressure Relief Valve (PRV) is designed to be opened to release pressure (Relief Overpressure) at Set Pressure is set, which follows the Requirement of ASME Section I Power Boiler to Pressure Relief Valve (PRV) is a deviation ( of Tolerance) of Opening. Pressure from Set Pressure not exceeding the value in the table divided by Set Pressure of the PRV.

Refer to: What is PRV pop test? (Popping test)

Beside this term, there’s Blowdown and Overpressure Tolerance for PRV testing:

Refer to: What is PRV blowdown?