An axis mundi is the center of the world. Eliade uses this term to help differentiate what is ‘sacred’ from what is ‘profane,’ whether that is in space or time. Profane is a state of chaos and meaninglessness.
An axis mundi makes something have meaning in the world of absolute reality.
From Eliade, “‘The Phenomenology of Religion,’ from The Myth of the Eternal Return” in God. Ed. Robinson. 2nd ed. Hackett, 2003.