An issue tracker is the software in which a software team lists every piece of work it has to do, as tickets. Each ticket says what has to be fixed or built, who is doing it and how far it has got. It is also called a bug tracker, a ticketing tool or a project tracker. Jira is the best-known one.
A ticket is one record in the tracker. It has a short title, a description, a priority, the person it is assigned to and a status. The status moves through fixed columns, such as "To do", "In progress", "In review" and "Done". The team sees these columns on a board, with one card for each ticket. Many teams plan in sprints, fixed blocks of two weeks. At the start of each sprint, the team chooses which tickets it will finish.
Consider a team in Chennai that builds a bus-ticket booking app. A passenger cancels a seat, but the app still shows the seat as taken. The tester who finds this opens ticket BUS-482: "Cancelled seat not released". She attaches a screenshot, the steps to repeat the problem and the phone model. The team lead sets the priority to High and assigns the ticket to a developer.
The developer puts the ticket number in the message of her code change, for example "BUS-482: release seat on cancel". The code repository reads that number and links the change to the ticket. So the ticket shows the exact code that fixed it. When the change is approved and merged, the tracker moves the ticket to "Done" by itself. When the CI/CD pipeline releases the fix to customers, it adds the release number to the ticket too.
Tickets also arrive from outside the engineering team. Say a passenger complains to customer support. Support records the complaint in the company's IT service management (ITSM) system. If the complaint turns out to be a bug, the support executive creates a linked engineering ticket. When engineering closes it, the support ticket is updated, and the passenger can be told.
Why does this matter? The tracker is the team's shared record. Without it, work is agreed in chats and calls, and nobody knows which bugs are still open. Managers read reports from the tracker, such as how many days a ticket takes from "In progress" to "Done". That figure is called cycle time, and it is one input to developer productivity metrics.
Companies often add features to the tracker with add-ons from a marketplace, called issue tracker plugins. An issue tracker for software work is different from an ITSM tool. The issue tracker plans the work that engineers do. The ITSM tool tracks requests for help from employees and customers.