What is the meaning of Igloo?

A dome-shaped Inuit shelter, constructed of blocks cut from snow.

A cavity, or excavation, made in the snow by a seal, over its breathing hole in the sea ice.

A reinforced bunker for the storage of nuclear weapons.

A kind of airfreight cargo container.

igloo

igloo (dome-shaped Inuit shelter, constructed of blocks cut from snow)

an igloo (snow shelter)

Source: wiktionary.org