polar motion

the motion of the Earth’s pole with respect to the ITRS. The main components are the Chandlerian free motion with a period of approximately 430 days, and an annual motion. It also includes sub-daily variations caused by ocean tides and periodic motions driven by gravitational torques with periods less than two days. Sub-daily variations are not included in the values distributed by the IERS, and are therefore to be added, after interpolation to the date of interest, using a model provided by the IERS Conventions.

Source: IERS Technical Note 36: Glossary (PDF, 244KB, Not barrier-free file.) of the IERS Conventions (2010)

Original Source: IAU 2006 NFA Glossary