There are a number of concepts which were first introduced in the physics literature (usually in an ad-hoc manner) to solve or simplify a particular problem, but later proven rigorously and adopted as general mathematical tools.
One example is the Dirac delta "function" which was used to simplify integrals, but at the time was perhaps not very well-defined to any mathematica standard. However, it now fits well within the theory of distributions. Perhaps another example is Newton's calculus, inspired by fundamental questions in physics.
Are there any other examples of mathematical concepts being inspired by work in physics?
Lets go with the most basic one first: $\color{red}{\text{Numbers}}$