The geoid is a model of Earth's shape that represents its mean sea level and gravitational field. It is an irregular, three-dimensional surface that accounts for variations in Earth's density and topography. The geoid helps scientists understand how gravity varies across the planet and is essential for accurate measurements in fields like geodesy and oceanography. Unlike a perfect sphere, the geoid is influenced by mountains, valleys, and ocean depths. It serves as a reference point for measuring elevation and depth, making it crucial for mapping and navigation. Understanding the geoid aids in various applications, including satellite positioning and climate studies.