GOST 12836 FLANGE tells you that flanges are referred to as flanges, which are just a general term, usually referring to the opening of several fixing holes around a disk-like metal body for connecting other things. This thing is widely used in machinery, so it looks strange, as long as it looks like a flange.

GOST 12836 FLANGE tells you that any connection parts that are bolted at the periphery of two planes and closed at the same time are generally called "flanges", such as the connection of ventilation ducts, such parts can be called "flange parts".
GOST 12836 FLANGE tells you that this connection is only a part of the equipment, such as the connection between the flange and the water pump, it is not good to call the water pump "flange parts". Smaller ones, such as valves, can be called "flange parts".
GOST 12836 FLANGE tells you that flanges are used for the connection between the motor and the reducer, and between the reducer and other equipment.
The above information is the GOST 12836 FLANGE manufacturer's introduction and analysis of the characteristics of the flange, hope it helps you.