The most popular style of disc springs, Bellevilles are cone-shaped discs which elastically deform to a shorter height when subjected to a load along the axis of symmetry. This elastic deformation characterizes spring action.
Disc Spring Basics
Belleville washers and other disc spring styles can be used singly or in stacks to achieve a desired load and travel. In general, they function best under conditions requiring very high load in confined space or short travel. Under these constraints, it is often not practical or even possible to use a coil spring.