In particle theory, the skyrmion is a topologically stable field configuration of a certain class of non-linear sigma models. The term was first used in 1979 to name a model of the nucleon by proposed in 1961 by Tony Skyrme. As a topological soliton in the pion field, it has the remarkable property of being able to model, with reasonable accuracy, multiple low-energy properties of the nucleon, simply by fixing the nucleon radius. It has since found application in solid-state physics, as well as having ties to certain areas of string theory.