A Crust

1. A more solid, dense or hard layer on a surface or boundary.
2. The external, hardened layer of certain foodstuffs, including most types of bread, fried meat, etc.
3. An outer layer composed of pastry
4. The bread-like base of a pizza.
5. (geology) The outermost layer of the lithosphere of the Earth.
6. The shell of crabs, lobsters, etc.
7. (uncountable) Nerve, gall.
8. crust punk (a subgenre of punk music)