Included within split path testing are multi step checkout paths, product recommendations, multi page forms. It also refers to where an A/Bn test changes multiple sequential pages instead of a single page. This is used for multiple step registration forms, wizards and checkout forms. The benefit of split path testing is that it creates a consistent experience through the whole path which allows the ability to change the order of input fields and steps across the journey which is unique to this type of testing.
It is a way of comparing multiple versions of a web page to find out which one converts the best. This is often used within marketing to test changes to registration pages, signup forms, calls to action or design in order to determine which method will lead to more sales.