An issue tracker is a system for recording, prioritizing, and following bugs and feature requests through their lifecycle. It is, in effect, the shared to-do list and long-term memory of a software project: a place where anything that is broken, missing, or proposed gets written down so it is not lost.
Bugzilla, one of the earliest widely used examples, describes itself on its own site as a defect-tracking system that lets teams keep track of outstanding bugs, issues, and enhancement requests in their products. The core idea is that each problem becomes a discrete record that can be assigned, discussed, and resolved.
Modern hosting platforms fold this directly into the code. GitHub’s documentation describes issues as a way to “track bug reports, new features and ideas, and anything else you need to write down or discuss with your team,” and notes they can be assigned, labeled, organized into milestones, and linked to pull requests.
Issue trackers matter because they turn informal, conceptual or concrete work into trackable, discussable units. They let large groups coordinate without losing context, and they create a durable history of what was decided and why - the difference between a project that remembers its decisions and one that keeps rediscovering the same bugs.