The crust of a piece of bread is the edge where it is harder and darker.

The crust is also the outermost layer of the earth. This is the solid layer people live on. It is generally less dense (heavy) than the deeper layers, so the crust floats on them.

It is made up of two parts: continental crust and oceanic crust. The continental crust forms continents. The oceanic crust forms most of the ocean floor.

It can also refer to the outer layers of other planets.

Crust