"Pipeline as a code" - is a relatively new approach that allows you to configure the deployment pipeline with code instead of manually configuring the running CI service. This concept is very popular today and I know at least five players in this segment: LambdaCD, Concourse, Drone, GoCD and Travis CI. This approach not only makes it easier to automate continuous integration and continuous deployment, but also allows you to test the infrastructure for deployment. This concept made the world look different, but the most important thing is that it really allows you to use CI more efficiently and elegantly.
Teams are pushing for automation across their environments(testing), including their development infrastructure. Pipelines as code is defining the deployment pipeline through code instead of configuring a running CI/CD tool. LambdaCD, Drone, GoCD and Concourse are examples that allow usage of this technique. From Thoughworks TechRadar
Jenkins approach is to have Groovy files, where most of the other players use yaml.
This is just a picture of this link from March 1, 2018
