A rigid block of crust and upper mantle-rock is known as a lithospheric plate.

Here's why:

* Lithosphere: This refers to the Earth's rigid outer layer, composed of the crust and the uppermost, solid part of the mantle.

* Plate: The lithosphere is broken into large, moving pieces called plates.

These plates are constantly in motion, interacting with each other in various ways (e.g., colliding, separating, sliding past) which drive geological phenomena like earthquakes, volcanoes, and mountain formation.