Which term describes the actual shape of Earth that is too complex to model exactly?

The term that accurately describes the actual shape of Earth, which is too complex to model exactly, is best understood as the "Surface of the Earth." This term encompasses the varied and irregular forms of the Earth’s surface, including mountains, valleys, rivers, and other geographic features.

While the other options refer to specific models or representations of the Earth, they do not capture the inherent complexity of its physical shape. The geometrical shape is a more abstract concept that doesn't accommodate the natural variability of the Earth's surface. The ellipsoidal model simplifies the Earth's shape to a mathematically defined surface, which is suitable for many calculations but does not reflect the natural topography. Similarly, the topographical model specifically represents features such as elevation and terrain but is still a simplification rather than an accurate depiction of the Earth's overall shape. Thus, the term "Surface of the Earth" effectively conveys the concept of a complex, irregular shape influenced by numerous geological and environmental factors.