Jenkins is a deployment tool and contains a lot of plugins to make it easy to build or test software. We use this for all our DEV, TEST, UAT and PROD systems. Jenkins provides a clear list of all the different jobs and they are easily accessible.
Jenkins Pipeline ("Pipeline") is a suite of plugins that supports the implementation and integration of continuous delivery pipelines in Jenkins. Pipeline offers a set of tools for modeling simple to complex pipelines "as code" through the Pipeline domain-specific language (DSL) syntax.
The definition of a Jenkins pipeline is written in a text file (Jenkinsfile) which in turn can be captured in GIT. This is the basis of "Pipeline-as-code", the Pipeline becomes part of your code.