Business Process Procedure
BPP is Business Process Procedure. It is created at the time of configuration and it helps other Consultants to know what has been configured in the system and what is the scope of that implementation anyways try to ignore such term called as Normal Clearing items. I guess you might be misinterpreting. It should be Normal clearing which is like processing items like we normally do that.
I guess this will help out to solve your issues related to it.