Traceability
Traceability is the ability to link related project artifacts together — a requirement to its test cases, a test case to a defect, a defect to the code change that fixed it — creating an auditable chain that answers "why does this exist" and "what does this affect" for anything in the system.
Traceability shows up most concretely as the Requirements Traceability Matrix, but the underlying idea extends further — a bug tracker linking a defect to the specific commit that fixed it, or a test case management tool linking a failed automated test directly to the user story it verifies, are both traceability in the same sense.
Its value compounds during change: when a requirement changes, traceability instantly shows every test case that needs review; when a test fails, traceability shows exactly which requirement or user story is now at risk — without it, both questions require manual, time-consuming digging through scattered documentation.
