Exactly what makes a MOPAR a "Matching Numbers" car?

I was watching an episode of Graveyard Carz where Mark was talking about 'matching numbers' on a 70 Barracuda. The engine and transmission matched the VIN and stampings on the body in a few places. But then other problems popped up that eventually revealed the Cuda was two cars grafted together. Then there was another episode where he was talking about things that are date coded. As I remember, intake manifolds, exhaust manifolds, distributors carbs plug wires, water pumps, heads and more had casting numbers and date codes.
It got me to thinking, exactly what does it mean when a car (in this case specifically a MOPAR) is "Matching Numbers"? I assume there are probably differences between different years, but in general, what makes a car a matching numbers car?
1. If the numbers stamped in the pad on the engine block, numbers stamped on the transmission and numbers stamped into the body on the radiator support and trunk opening lip (on my 69 Barracuda) match the VIN, is that a matching number car? Or do parts with numbers cast into them (like manifolds, water pumps, heads, etc.) need to match. For instance, a 1971 340 intake manifold might fit my 69 340 and look fine when painted, but it might have a different casting number.
2. Then factor in date coded parts as mentioned above. Do all these parts need to also be correct in order for a car to be considered matching numbers?
3. Are there different levels of what is considered to be Matching Numbers?
What do you guys think?