A sipapuni (sometimes "sipapu") is a "place of emergence" in the creation myths of a number of indigenous American peoples ("Indians"), specifically the region now known as the southwest United States (Arizona, New Mexico, the Grand Canyon). These tribes include the Zuni, Hopi, and Navajo.
A sipapuni can be literal indentation in the earth, perhaps created through a variety of geological processes, an artificial hole in a ritual space (a "kiva"), or simply a mythological idea. In the myths, a sipapuni is also a "hole in the sky". (The "sky" is viewed as a hard shell.) Proto-human entities move from realms of darkness or chaos through this hole, to escape to a "higher" world. In one myth, these entities are threatened by a great flood on all sides, and fly through a hole revealed to them by another being. Typically, the beings move through three worlds until they arrive at the fourth world, where they become human beings.
So the sipapuni allows humans to come "out" of the ground into the world of sunlight and human civilization.