An igloo (or iglu) is a shelter (a place for people to stay warm and dry) made from blocks of snow placed on top of each other, often in the shape of a dome (like half of a hollow ball). They were used in winter as temporary shelters by hunters when they were away from their regular homes.
They were most often built in places where a lot of snow covers the land for weeks or months at a time, such as the far north of Canada and Greenland. Most igloos are built by native Inuit people (sometimes called Eskimoes). As they learned to build them better, sometimes people would build larger igloos that would last longer and hold more people, even for dancing.