Learn in the textbookSecure Development (By-Design Principles and Vulnerability Countermeasures)
DefinitionA security patch (セキュリティパッチ) is an update program that the vendor provides to fix a vulnerability found in software such as an OS or an application.
ExplanationVulnerabilities keep turning up after a product is released, so applying a patch promptly once it is out is the basic countermeasure in operations and maintenance. Leaving it unapplied makes a system an easy target for attacks on vulnerabilities whose methods are widely known.
AnalogyIt is like an inspection turning up a faulty window lock, which you then fix with a replacement part sent by the maker.
Memory hookA patch is a piece of cloth sewn over a hole, so picture it covering the hole that is the vulnerability.