This answer is going to differ between people.
I feel like I'm cheating when I say that my CB750 is a "restoration" since many people ask about it when I take it out. It's faster to say that then to overburden the listener of what all I did and didn't do, but I don't feel like I'm using the right word. I technically call it more of a refurbishment, though in some minds it's "restored."
So what does a restoration mean to you?
A restoration to me means what the word implies: It's been "restored" to the condition that it was when new, but not necessarily have to be the same exact specifications (I believe you can have different handlebars, paint scheme, etc and still stay "restored" but not "original").
That means the engine must be at full compression. I didn't touch my CB750 engine. That also means that the frame should also be repainted (or powder coated) which I didn't do. Or maybe my bike is truly "restored" but it isn't a "frame off restoration", which is another term.