The official name of the country is the Netherlands. In the rest of the world, the name Holland is commonly used for the entire country. However, when used correctly, the name Holland only refers to the area covered by the provinces of North and South Holland.
Indeed, in this area, which contains the largest cities and largest part of the population, this use is common as well. However, outside of this area, and particularly in the South and North, this use is often considered quite insulting, and the Netherlands is preferred. Consider how a Scot would feel if called English. In these areas, you are likely to be corrected with a slightly annoyed explanation of the difference between Holland and the Netherlands.