I understand Engineering as the Design, Development, Build, Operation and/or Support - whichever applies - of technical Products as well as Systems of End-Products.

Products include 

• Parts
• Components
• Systems, and 
• End-Products.

A Part is a hardware item, which is not integrated with any other item, and which cannot be disintegrated other than by destruction. 

A hardware item created via integration (e.g. assembly, installation, welding) of any of Parts, other Components, or hardening materials such as binders and fillers, is called a Component.

A System is an assembly and/or installation of Parts and Components (possibly with software integrated) intended to deliver defined functions to a client. Examples include pumps, valves, car engines.

An End-Product is a System, or an assembly and/or installation of Systems, intended to deliver functionalities* to a client, who usually is acting as its operator. The End-Product is not intended to be subjected to any further assembly or installation processes. It can be broken down into System(s), Components and Parts. Examples include sub-marines, ships, oil platforms, power plants, washing machines, television sets, cars, aircraft and spacecraft - to name just a few.

A System of End-Products can then be seen as a set of End-Products intentionally connected to each other to ensure operability of at least one of its End-Product members. Examples include a spacecraft with its ground station (i.e. representing two distinct End-Products) and the air transportation system with aircraft and airports. I do not regard a System of End-Products in its entirety as a Product on its own.