What is Refactoring?
Restructuring existing code to improve its design and readability without changing its external behavior.
Definition
Refactoring, systematized in Martin Fowler's catalog, is behavior-preserving transformation: extract function, rename variable, inline abstraction, replace conditional with polymorphism—each a small, reversible step verified by a passing test suite, which is the non-negotiable safety net. IDEs like IntelliJ and VS Code automate the mechanical moves reliably; language servers make renames project-wide and safe. Refactoring works best woven into daily work (the boy-scout rule, preparatory refactoring before a feature: "make the change easy, then make the easy change") rather than as big-bang rewrites. It is the primary mechanism for servicing technical debt and keeping designs malleable as requirements shift.