In physics, a non-invertible symmetry is a symmetry of a quantum field theory that is not described by a group, and which in particular does not have an inverse.

External links 
 "ICTP Lectures on (Non-)Invertible Generalized Symmetries" by Sakura Schafer-Nameki
 "A New Kind of Symmetry Shakes Up Physics" by Kevin Hartnett, Quanta Magazine
 "Non-Invertible Symmetries and their Representations", video lecture by Sahand Seifnashri at Institute for Advanced Study

Quantum field theory