An exciton is a bound state of an electron and a hole in a semiconductor or insulator. It is a quasiparticle, meaning that it has some of the properties of a particle, such as mass and energy, but it behaves differently from a traditional particle in some ways. For example, excitons cannot move freely through a material in the same way that electrons and holes can.

An excitation, on the other hand, is a more general term that refers to any change in the energy state of an atom or molecule. Excitations can occur for a variety of reasons, such as the absorption of light or the collision of two particles. When an atom or molecule is excited, its electron is promoted to a higher energy level.