Integrable system
In mathematics, integrability is a property of certain dynamical systems, that means very roughly that the solutions of the system are "simple" enough that they can be written down exactly (in principle). More precisely, while there are several distinct formal definitions, an integrable system can be thought of as a dynamical system with sufficiently many conserved quantities, or first integrals, that its motion is confined to a submanifold of much smaller dimensionality than that of its phase space.