Gasoil D2 - Fuel Oil is a fraction obtained from petroleum distillation, either as a distillate or a residue.
Detailed introduction to RUSSIAN GASOIL L0.02-62/D2 GOST 305-82:
Gasoil D2 - Fuel Oil is made of long hydrocarbon chains, particularly alkanes, cycloalkanes and aromatics. The term fuel oil is also used in a stricter sense to refer only to the heaviest commercial fuel that can be obtained from crude oil, heavier than gasoline and naphtha.
Gasoil D2 - Fuel Oil is any liquid petroleum product that is burned in a furnace or boiler for the generation of heat or used in an engine for the generation of power, except oils having a flash point of approximately 40 °C (104 °F) and oils burned in cotton or wool-wick burners. In this sense, diesel is a type of fuel oil.