The term "crust" is often used in different contexts, so it depends on what you're referring to. Here are a few possibilities:

In geology:

* Lithosphere: This refers to the rigid outer layer of Earth, which includes the crust and the uppermost part of the mantle.

In cooking:

* Outer layer: This is the most common alternative name for crust, especially when referring to baked goods like bread, pizza, or pies.

* Bottom layer: This term is used when referring to the bottom part of a crust, especially in pies.

In other contexts:

* Shell: In some cases, "crust" can be used synonymously with "shell," like in "the crust of a bread loaf" or "the crust of an earthworm's body."

To clarify, please provide more context about what kind of "crust" you're asking about.