What is the difference between Set Id and a Business Unit?

Where a Business Unit organizes your company or your organization, SetIDs
help you organize your data within the system. The HRMS system uses tables
(Control Tables or Prompt Tables) that use a high-level key that enables
you to identify and retrieve data from the system. A secondary high-level
key,referred to as a SetID, has also been added on various tables. SetIDs are
simply the labels used to identify a TableSet. Business Unit and SetID
functionality in PeopleSoft also provides you with a higher business

level for reporting purposes and other business data roll-up.