An issue is something that is raised by anyone on the project. Issues are something that has been unresolved; is causing a problem; or that raises a question. It is information that is incomplete. An item that needs clarification or further investigation. How do you track them?
When you first come across Project Management as a methodology it is not always easy to understand the difference between this (as a methodology) and the number of other methodologies out there. People often confuse what are process improvement methods with project management frameworks.