The Scriptable Render Pipeline (SRP) is a Unity feature that allows you to write C# scripts to control the way Unity renders each frame. SRP Core is a package that makes it easier to create or customize an SRP.
SRP Core contains reusable code, including boilerplate code for working with platform-specific graphics APIs, utility functions for common rendering operations, and the shader libraries used in the High Definition Render Pipeline (HDRP) and Universal Render Pipeline (URP).
If you are creating a custom SRP from scratch or customizing a prebuilt SRP, using SRP Core will save you time.
For more information on SRP, including a guide to getting started with a custom SRP, see the SRP documentation. For more information on Unity's prebuilt SRPs, see the Universal Render Pipeline (URP) documentation, or the High Definition Render Pipeline (HDRP) documentation.