A render pipeline performs a series of operations that take the contents of a Scene, and displays them on a screen. At a high level, these operations are:
Different render pipelines have different capabilities and performance characteristics, and are suitable for different games, applications, and platforms.
It can be difficult to switch a Project from one render pipeline to another, because different render pipelines use different shader outputs, and might not have the same features. It is therefore important to understand the different render pipelines that Unity provides, so that you can make the right decision for your project early in development.
Unity offers the following render pipelines: