Definition of "navel"

Within the navel of this hideous wood,Immured in cypress shades, a sorcerer dwells,Of Bacchus and Circe born, great Comus

1637, John Milton, A Mask presented at Ludlow Castle, 1634

We sat alfresco on the edge of a “square,” in reality a pond of cobbly mud with a plinth plonked in its navel […]

2004, David Mitchell, Cloud Atlas, London: Hodder and Stoughton

This contributed to a rapid rise in planted acreage in northern California, especially in navels, which are more suited to growing conditions there.

1981, Peter K. Thor, Edward V. Jesse, Economic Effects of Terminating Federal Marketing Orders for California-Arizona Oranges