A pull request (PR) is a GitHub mechanism for proposing changes from one branch to another, combining review and discussion before merging. A pull request displays the diff between branches, allows inline comments on specific lines, and can trigger automated checks (CI/CD pipelines, linters, test suites) that must pass before merging is permitted. Reviewers can approve, request changes, or leave general feedback, and the pull request tracks the full conversation history. Pull requests serve as a coordination point: they make proposed changes visible to all collaborators before those changes take effect, reducing the risk of unreviewed or conflicting work entering the main development line.