RP is a series of operations that take the contents of a Scene and displays them on a screen. At a high level, these operations are Culling, Rendering, and Post-Processing. It’s difficult to switch from one to another RP because the shader outputs varies and might not have the same feature. We can custom shaders in different piplelines, but the ultimate effect may be different. Unity has Built-In, Universal, and High Definition and Scriptable RP. Scriptable RP allows creating RP from scratch or modifying URP/HDRP.
*what is high definition? video of higher resolution and quality than standard-definition is HD, but there’s no standardized meaning for HD. Generally any video image with considerably over 480 scan lines or 576 vertical lines is considered HD.