The Lithosphere-Asthenosphere Boundary (LAB) is the depth at which the Earth’s rigid lithosphere transitions into the more ductile asthenosphere. This boundary is critical in understanding plate tectonics, as it marks the zone where tectonic plates move over the more fluid asthenosphere, influencing the dynamics of plate movement.
Source Schubert, G., Turcotte, D. L., & Olson, P. (2001). “Mantle Convection in the Earth and Planets.” Cambridge University Press.