Wikipedia sums it up quite nicely:
Holland is a name in common usage given to a region in the western part of the Netherlands. The term Holland is also frequently used as a pars pro toto to refer to the whole of the Netherlands. This usage is generally accepted but disliked by many Dutch people in the other parts of the Netherlands.
It's funny that many people who live in the Netherlands would not deny being a Hollander, even if they do not live in North- or South-Holland.
And especially during a soccer match against Germany :-).

