Rind

Etymology

From Old English "rinde" (bark, crust), of Germanic origin. The word first named tree bark and later stretched to any tough outer casing, from a wheel of cheese to a slab of pork.

noun · /RYND/
The tough or firm outer layer of a fruit, cheese, or cut of bacon.
What it names
The protective skin that has to be dealt with — cut away, left on, or eaten — depending on the food.
Example
Don’t throw out the parmesan rind — simmer it in soup to add savory depth.
Related idea
On citrus the rind splits into two: the flavorful zest on the outside and the bitter pith within, so “rind” names the whole skin while those two name its layers.