Code that most likely does what the developer wanted it to do, but which is too clumsy and can be shortened.
Code that may be incorrect.
Performance issues are generally related to code that does things that are superfluous; i.e., which - except from using time and memory - have no meaningful sideeffect compared to a simpler solution.
Collection of predefined issue categories where each category describes the quality property of the software that is affected by the issue.