(名詞/形容詞) 從未被修復的已知軟體瑕疵 (的) - 尤指暴露安全漏洞的軟體瑕疵。名詞亦寫成 forever day

Forever day is a play on "zero day," a phrase used to classify vulnerabilities that come under attack before the responsible manufacturer has issued a patch. Also called iDays, or "infinite days" by some researchers, forever days refer to bugs that never get fixed—even when they're acknowledged by the company that developed the software.
—Dan Goodin, "Rise of 'forever day' bugs in industrial systems threatens critical infrastructure," Ars Technica, April 9, 2012

To make matters worse, many industrial control system vendors are not committed to fixing the security holes that exist in their deployed products, especially legacy products, resulting in what are called "forever-day bugs".
—"Special Track: Cyber and Smart Grid Information Security" (PDF), The 2013 International Conference on Security and Management, February 21, 2013