Issue tracking manages and maintains lists of issues, needed by your business. It can be used as a Customer Service support call center to create, update, and resolve reported customer issues, or even issues reported by your companay's other employees.
It also contains a knowledge base which can be used to store information on each customer, resolutions to common problems, or any other such data.
An issue is a running report on a particular problem, its status, and other relevant data. Issues can have several aspects to them. Each issue may have an urgency value assigned to it, based on the overall importance of that issue.