Crusts meaning : A more solid, dense or hard layer on a surface or boundary. The external, hardened layer of certain foodstuffs, including most types of bread, fried meat, etc. An outer layer composed of pastry The bread-like base of a pizza. The outermost layer of the lithosphere of the Earth. The shell of crabs, lobsters, etc. Nerve, gall. A living. To cover with a crust. To form a crust. A subgenre of punk rock, derived from hardcore punk with extreme metal elements, often with pessimistic lyrics about political and social ills.