[alistairSH]

Holland is a region within the Netherlands. It is (was?) the most populous and economically productive region, so over time got used as a substitute for Netherlands.

"Dutch" is derived from a word that means "the people". As is the Deutsch in Deutschland (what Germans call their nation - land of the people, basically). At one time, there were high Dutch and low Dutch, describing people from hilly regions in (what is now) Germany and people from the low-lying area that is now the Netherlands.

Netherlands is just what it sounds like - the low lands. Apt, since so much of the country should be underwater.

[wholien]

You see "nether-" in other words too, like "netherworld" or "nether regions", which both mean low/lowest parts of a place.