Sea level represents the average height of the ocean surface relative to a defined datum, typically measured by tide gauges or global satellite altimetry. This level is influenced by several dynamic processes, including changes in the volume of water in the global ocean system. The primary factors controlling these changes include the melting of continental ice sheets and glaciers, and the thermal expansion of seawater as it warms. Global fluctuations in sea level occur over various timescales, ranging from Milankovitch cycles, which drive eustatic changes over millennia, to localized adjustments due to crustal plate tectonics. Understanding these physical processes is critical for modeling coastal geology, ocean circulation, and the long-term interaction between landmasses and marine environments.