The term that describes down-dropped blocks of crust bounded by steeply dipping normal faults is graben.

Here's a breakdown:

* Graben: A graben is a geological feature consisting of a block of land that has been lowered relative to the surrounding land due to extensional tectonic forces. These forces create normal faults, where the hanging wall (the block above the fault) moves down relative to the footwall (the block below the fault).

* Normal faults: These faults are characterized by a hanging wall that slides down relative to the footwall. This downward movement creates the space for the graben to form.

Example: The Rhine Graben in Europe is a classic example of this geological feature.