Refactoring (noun) : a change made to the internal structure of software to make it easier to understand and cheaper to modify without changing the observable behavior of the software.
To Refactor (verb) : to restructure software by applying a series of refactorings without changing the observable behavior of the software.

p. 33-43 as cited in: Militiadis Lytras, Patricia Ordóñez de Pablos, Ernesto Damiani (2011) Semantic Web Personalization and Context Awareness. p. 111 - Refactoring: Improving the Design of Existing Code, 1999