Holland is the richest and the second coolest part of The Netherlands. 'Holland' is often taken to be the entirety of the Netherlands, much like England and the United Kingdom. This is mainly the result of the fact that Holland has been the politically and culturally dominant province of the Netherlands since the Eighty Years' War - after all, the Hague and Amsterdam are both located in Holland, all the main harbours of the Netherlands are in Holland or Zeeland (the latter has been defacto part of Holland since the Medieval Ages), and standard Dutch is based on a Hollandish dialect.
During the Medieval Ages, there was a rather bitter rivalry between Holland and Frisia, which eventually resulted in Holland conquering West Friesland (which has been the northernmost part of Holland ever since), and Frisia permanently losing its position as the dominant power in the northern half of the Low Countries. (this old Hollandish-Frisian rivalry is also one of the reasons why Frisia/Friesland is so understated compared to Holland - history is written by the winners, after all)
The Medieval county of Holland also had frequent conflicts with its southern neighbour, the county of Flanders, over the rich and strategically important county of Zeeland, which also ended in Holland incorporating Zeeland (though the latter nominally continued to exist as a separate county and province).
Unlike the British, most Dutch generally don't seem to mind this Holland-Netherlands confusion much.
Exceptions on this are typically patriottic Frisians or people from Noord Brabant and Limburg, two provinces of the Netherlands that has never really fitted in with the rest, as the local population was and still is predominately Catholic.