This document discusses code smells, which are signs of deeper problems in code that can negatively impact design quality and maintenance. It identifies several code smells including duplicated code, long methods, large classes, long parameter lists, divergent change, shotgun surgery, feature envy, data clumps, primitive obsession, switch statements, lazy class, speculative generality, temporary fields, and message chains. For each smell, it provides a brief refactoring recommendation such as extracting methods or classes to improve code structure, readability, and flexibility.