Pipelines run tasks in a sequence that is abstracted as a Directed Acyclic Graph. You are free to define a granular pipeline that performs a specific vertical of the DevOps workflow (such as quality testing) or you can package all of it into one single pipelines.
Pipelines give you the flexibility to define templates that an organisation adheres to. For further reading please check the official documentation of tekton
Pipelines are templated entities. The instances of their execution are defined by the PipelineRun object