Let's say I build an ECU. There will be perhaps a couple of PCBs, the connectors between then, the box it goes in, the fixings for mounting the PCBs in the box. And let's add the connectors that plug into the interfaces (but no cables since we don't know where this is going). That's a project, right?
OK, now lets build a car and fit it with wheels and [...], and an ECU. Gosh, that car must be worthy of 'project' (and then some!) but what of the ECU? Is that no longer a project? Do we have to think up a new name for it because it's used in some bigger thing?
No, a 'project' is just an encompassing term for a particular planned aim, in this case the creation of an ECU. Or car. The files that make up a PCB would be a project. The files (spec sheet, manufacturing info, test results) that make up a resistor on the PCB would be a project.
So 'project' is actually the appropriate noun for a collection of files that comprise a thing, whether those are just the schematics and layouts, or include (or, perhaps, are just) the mechanical CAD files and other stuff. That thing may be the smallest part of the collection of a million components en route to the moon. It just depends on where you're standing as to what view you're seeing.