# Jenkins main pipeline concepts

This tutorial explains the main Jenkins main pipeline concepts.

Pipeline : In Jenkins, a pipeline is a collection of events or jobs which are interlinked with one another in a sequence. Entire Declarative pipeline script should be written inside the pipeline block. It’s a mandatory block.

Node : The node is a machine on which Jenkins runs is called a node. A node block is used in scripted pipeline syntax.

Stages : A stage includes all the work that needs to be done. The work is defined in the form of stages. Each stage executes a particular task. A stage has one or more steps.

Steps : A step in Jenkins defines what we have to do at a particular step in the process. There can be a series of steps within the stage.

Agent : An agent is a directive that enables the users to execute multiple projects within the same Jenkins instance by distributing the load. Moreover, we assign an executor to the build through an agent. You can either use a single agent for the entire pipeline or use a distinct agent for the different stages of the pipeline.

Here are some values used with agents:

• Any : Any of the available agents execute the pipeline.
• None : It is used at the pipeline root and implies no global agent, but each stage must specify its own agent.
• Label : Labeled agent is used to execute the pipeline or the specific stage.
• Docker : One can use the Docker images as the execution environment & specifying the agent as docker.