Code is considered "unused" if it has no effect on the outcome or functionality of the application. Unused code consists of any code that does not meet the following criteria:
1. Write a value to memory (such as parameters passed by reference and reference types)
2. Return a value (such as function return values)
3. Change the code's meaning (such as declaration statements)
4. Call a function.
5. Does not define a variable that is used by any statement that meets 1 - 4 above.
Having unused code in your application can use excess system resources, detrimentally affect performance, and make code difficult to understand and maintain.