Defect linking
The connection between a test result and the bug record it produced in the issue tracker. Two-way linking means the tester sees the bug from the result and the developer sees the failing case from the bug. Without it, the question of which tests fail because of a given open bug has no answer short of asking people.
Also called: Bug linking, Issue linking
What the link makes possible
With links in place, three questions answer themselves. Which open bugs are blocking this release's tests. Which of today's failures are already known. And the one that sets the retest list: which cases to rerun now that a bug is marked fixed. Without links those answers live in run comments and in people's heads, and the retest list is reconstructed from memory the day before release.
Link from the result, not only the case
A bug is found in an execution: a specific build, environment and run. A link on the result keeps that context, so a reader can see that the case failed on the staging build of 14 October and passed after the fix. A link held only on the test case loses it, and the case keeps pointing at a closed bug long after anyone remembers why.
One way and two way
One-way linking stores the ticket key on the result and shows the ticket's status in the test tool. Two-way linking also writes back to the tracker, so the ticket shows which cases cover it and how they last ran. The second half matters because developers rarely open the test management tool. If coverage is only visible there, it is invisible to the people fixing the bug.
Where it breaks down
A ticket key pasted into a comment field is a link for humans only; no report can count it. One bug that breaks twelve cases should be one ticket linked twelve times, not twelve tickets. And when every bug is filed through a shared tracker account, the tracker loses who actually found it unless the description names the reporter.
In QAM Hub
On every plan you can file a new issue or link an existing one from a test execution at any status or from a checklist cell, attach several tickets to one execution, and link one ticket to many selected cases at once. Linked issues stay visible on the case, the run and the Defects report. On Standard and Advanced the integration is two-way: each linked issue gets a QAM Hub comment listing the test cases that cover it, their latest results and the bugs found. Setup is in connecting an issue tracker.