This part of EN 16905 specifies the terms and definitions for the rating and performance calculation of gas-fired endothermic engine driven heat pumps for heating and/or cooling mode including the engine heat recovery, to be used outdoor. This European Standard specifies the terms and definitions. This European Standard is to be used in conjunction with the following standards: a) FprEN 16905-2:2022 on safety; b) EN 16905-3:2017 on test conditions; c) prEN 16905-4:2022 on the requirements, test conditions and test methods; d) FprEN 16905 5:2022 on the calculation of seasonal performances in heating and cooling mode; e) the heat pump standards, EN 14511 2, EN 14511-3 and EN 14825. This European Standard only applies to appliances with a maximum heat input (based on net calorific value) not exceeding 70 kW at standard rating conditions. This European Standard only applies to appliances under categories I2H, I2E, I2Er, I2R, I2E(S)B, I2L, I2LL, I2ELL, I2E(R)B, I2ESi, I2E(R), I3P, I3B, I3B/P, II2H3+, II2Er3+, II2H3B/P, II2L3B/P, II2E3B/P, II2ELL3B/P, II2L3P, II2H3P, II2E3P and II2Er3P according to EN 437. This European Standard only applies to appliances having: f) gas fired endothermic engines under the control of fully automatic control systems; g) closed system refrigerant circuits in which the refrigerant does not come into direct contact with the fluid to be cooled or heated; h) where the temperature of the heat transfer fluid of the heating system (heating water circuit) does not exceed 105 °C during normal operation; i) where the maximum operating pressure in the: 1) heating water circuit (if installed) does not exceed 6 bar 2) domestic hot water circuit (if installed) does not exceed 10 bar. This European Standard applies to GEHP appliances only when used for space heating or space cooling or for refrigeration, with or without heat recovery. This European Standard is applicable to GEHP appliances that are intended to be type tested. Requirements for GEHP appliances that are not type tested would need to be subject to further consideration.