In terms of geology, what does the term "asthenosphere" refer to?

The term "asthenosphere" specifically refers to a semi-fluid layer located beneath the lithosphere. This layer is part of the upper mantle and extends roughly from about 100 kilometers to 700 kilometers beneath the Earth's surface. The asthenosphere is characterized by its ability to flow slowly, which allows tectonic plates in the lithosphere above it to move. This movement is essential for the tectonic processes that shape the Earth's surface, such as earthquakes and the formation of mountains.

The distinction between the asthenosphere and the lithosphere is crucial; while the lithosphere is rigid and comprised of the crust and the uppermost solid mantle, the asthenosphere's semi-fluid nature enables it to respond to pressure and temperature changes. Thus, it plays a vital role in plate tectonics and the geological activity of the Earth.