[flohofwoe]

Exactly, the deeper you dig, the more the "engine" just disolves into lines of code. Where does the engine HAL end and where do operating system services begin? Is libcurl considered part of the engine? Maybe if it's linked to the engine code? But what if the curl libs are part of the OS installation?

And on the opposite end, if the Unity editor is considered part of the engine, why not Visual Studio, Photoshop and Maya/3dsMax/Blender too?

In the end, the engine is just that fuzzy layer between the high level gameplay code and the operating system (going with my own preference that "engine" should only be used for the runtime parts).