The "as code" paradigm is about being able to reproduce and/or restore a full environment within minutes based on recipes and automation, managed as code.
Most Jenkins users already use this approach to manage the architecture and infrastructure for applications they build and deploy with Jenkins. But what about your Jenkins master?
Shall we store the whole JENKINS_HOME in a Git repository ? Many use xml templates or Groovy voodoo to address this need. Early in 2018, we released the Jenkins configuration as code project, designed to offer a standard mechanism to setup Jenkins, without needs to know either the Jenkins internals or any piece of Groovy syntax. Just mimic the web UI...as code.