Just to stir it a bit, a Norwegian national park is “a large, untouched or mostly untouched, special or beautiful natural area in state ownership or adjacent areas in private ownership. In national parks, the natural environment must be preserved. The landscape together with its plants, animal life and natural and cultural remains is protected against improvement, building, pollution or any other intervention”. (my translation of the Norwegian law).
That is more or less the definition most countries use for a "national park".
In contrast, IMHO, British National Parks are only there to take money from tourists. Otherwise, they aren't worth sh*t.