TLDR: Extended maintenance refers to the support provided for software or systems beyond their standard lifecycle, ensuring continued security updates, patches, and compatibility improvements. This service is particularly critical for enterprises running legacy systems or long-term projects where immediate migration to newer versions is not feasible. Providers like Canonical and Red Hat offer extended maintenance options to help organizations maintain secure and stable environments.

https://en.wikipedia.org/wiki/Software_maintenance

Extended maintenance often includes features like security updates, bug fixes, and critical patches, but may exclude feature additions or non-essential updates. For instance, Canonical provides Extended Security Maintenance (ESM) for Ubuntu LTS versions, allowing organizations to receive essential updates beyond the typical five-year support window. This service is particularly useful for systems operating in regulated industries, where software reliability and security are paramount.

https://ubuntu.com/security/esm

The value of extended maintenance lies in its ability to provide organizations with the time needed to plan and execute migrations to newer systems without disrupting operations. While extended maintenance typically incurs additional costs, it offsets potential risks like security breaches and compliance violations. By bridging the gap between lifecycle transitions, extended maintenance helps enterprises sustain long-term infrastructure stability and operational continuity.

https://www.redhat.com/en/resources/extended-lifecycle-support