Releases of Ubuntu get a development codename (“Breezy Badger”) and are versioned by the year and month of delivery - for example Ubuntu 17.10 was released in October 2017. LTS or “Long Term Support” releases are published every two years in April. Every six months between LTS versions, Canonical publishes an interim release of Ubuntu. See this link for more details on the Ubuntu Release Cycle.

LTS releases are in “General Support” for 5 years and “Extended Security Maintenance” (see below) for an additional 5 years. Interim releases are supported for 9 months. Packages in main and restricted are supported for 5 years in long term support (LTS) releases. Ubuntu Flavors generally support their packages for 3 years in LTS releases but there are exceptions.

During the lifetime of an Ubuntu release, Canonical provides security maintenance. Basic Security Maintenance covers binary packages that reside in the main and restricted components of the Ubuntu archive, typically for a period of 5 years from LTS release.

Extended Security Maintenance (ESM) provides security updates on Ubuntu LTS releases for additional 5 years. It is available with the Ubuntu Pro subscription or a Free subscription. Please see the Ubuntu Website for details.

The dates for active and security support are taken from here what is used for the graph rendering on the Release Cycle Page.

Ubuntu Pro offers security fixes for critical, high, and selected medium CVEs in the main and universe repositories. Ubuntu Pro (Infra-only) - previously known as Ubuntu Advantage - only guarantees security fixes for packages in the main repository - other packages are on a best-effort basis.

For package specific support details, run the ubuntu-security-status command (ubuntu-support-status on versions before 20.04).