An Extended Service Branch (ESB) is an option available starting with Horizon 7.5, VMware App Volumes 2.14, and VMware User Environment Manager 9.4.0. It contains periodic service pack (SP) updates, which include cumulative, critical bug fixes, and security fixes.
If you decide not to upgrade to the latest version of Horizon, and instead remain on the same version, you can deploy an ESB and continue to receive timely bug and security fixes. The SP updates do not include new features, so you can rely on a stable Horizon platform for your critical deployments.
Separate ESBs are available once a year for the core Horizon platform, VMware App Volumes, and VMware User Environment Manager. ESBs are supported for 24 months with three scheduled SP updates: SP1 will be released six months after the initial release, SP2 will be released three months after SP1, and SP3 will be released six months after SP2.
For more information, see FAQ: Horizon 7, App Volumes, UEM Extended Service Branches (ESB) https://kb.vmware.com/s/article/52845.