Code smell, also known as bad smell, in computer programming code, refers to any symptom in the source code of a program that possibly indicates a deeper problem. According to Martin Fowler, "a code smell is a surface indication that usually corresponds to a deeper problem in the system". Another way to look at smells is with respect to principles and quality: "smells are certain structures in the code that indicate violation of fundamental design principles and negatively impact design quality". Code smells are usually not bugs—they are not technically incorrect and do not currently prevent the program from functioning. Instead, they indicate weaknesses in design that may be slowing down development or increasing the risk of bugs or failures in the future. Bad code smells are an important reason for technical debt. Robert C. Martin calls a list of code smells a "value system" for software craftsmanship.