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The Chandler wobble is the shifting of the exact position of the Earth's north and south poles on its surface, i.e., a shift in the axis of the Earth's rotation within the Earth itself. Such a wobble was predicted by Newton and Euler and confirmed much later by Seth Carlo Chandler in 1891. The shift follows a regular cycle with a period roughly 433 days, shifting the position of the poles on the order of 9 meters, which, for astronomers, affects positions on the celestial sphere by about a third of an arcsecond. Together with an additional, smaller nutation, it produces a 7-year cycle. These are independent of the precession of the equinoxes, the cyclic shifting of the Earth's axis by many degrees over the course of about 26000 years. The difference is that the precession is a change in the position within the celestial sphere pointed at by the Earth's poles, and the Chandler wobble is the shifting of these poles on the Earth's surface, i.e., a change in which line through Earth constitutes its axis of rotation.
Upon the confirmation of the wobble's existence, its period was not the expected value (305 days), the difference now attributed to the Earth's non-rigidity, especially the oceans. A mystery remains regarding the wobble in that it has now been determined to be something which would dissipate on a very short (68-year) timescale. The conclusion is something drives it to continue. Also, variation in the wobble has been detected since its discovery.
A Chandler wobble of Mars has been detected while mapping its surface.