outer shell
Definitions
The external covering or casing of an object, structure, or organism.
The outermost layer of a multi-layered system, often serving as a protective barrier.
Examples
The beetle has a hard outer shell that protects it from predators.
You must remove the tough outer shell of the coconut before you can access the meat inside.
The spacecraft's outer shell was designed to withstand the intense heat of atmospheric reentry.