• An equatorial bulge is a difference between the equatorial and polar diameters of a planet, due to the force exerted by its rotation. A rotating body tends to form an oblate spheroid rather than a sphere.
• The Earth has an equatorial bulge of 42.77 km (26.58 mi): that is, its diameter measured across the equatorial plane (12,756.27 km (7,926.38 mi)) is 42.77 km more than that measured between the poles (12,713.56 km (7,899.84 mi)).
• An observer standing at sea level on either pole, therefore, is 21.36 km closer to Earth’s centrepoint than if standing at sea level on the equator.
• The value of Earth’s radius may be approximated by the average of these radii.
• An often-cited result of Earth’s equatorial bulge is that the highest point on Earth, measured from the center outwards, is the peak of Mount Chimborazo in Ecuador, rather than Mount Everest.
• But since the ocean also bulges, like the Earth and the atmosphere, Chimborazo is not as high above sea level as Everest is.

Source: Wiki