This read-only integer carries a numeric error code for a failed package abort operation, the machine-readable counterpart to abortMessage. It's used by automation or admins to categorize why a rollback itself failed, which is a more serious situation than an ordinary deployment failure since it can leave the element in an inconsistent state. For example, a distinct abortError code for a partial rollback would flag to an admin that manual verification of the element's actual state is now needed, rather than assuming a clean pre-deployment state was restored.