In quantum field theory, the statistical mechanics of fields, and the theory of self-similar geometric structures, renormalization is any of a collection of techniques used to treat infinities arising in calculated quantities.
When describing space and time as a continuum, certain statistical and quantum mechanical constructions are ill defined. To define them, the continuum limit has to be taken carefully.
Renormalization establishes a relationship between parameters in the theory, when the parameters describing large distance scales differ from the parameters describing small distances. Renormalization was first developed in quantum electrodynamics (QED) to make sense of infinite integrals in perturbation theory. Initially viewed as a suspicious provisional procedure by some of its originators, renormalization eventually was embraced as an important and self-consistent tool in several fields of physics and mathematics.
Read more about Renormalization: Self-interactions in Classical Physics, Divergences in Quantum Electrodynamics, Renormalized and Bare Quantities, Regularization, Attitudes and Interpretation, Renormalizability, Renormalization Schemes, Application in Statistical Physics