I initially thought BAPIs were categorized as an interface, however, after reading about BDC on the scn wiki, I learned that BAPIs should be used over BDC when bringing in data whenever possible.
"BDC was a great way of uploading data into SAP in a pre-BAPI era, now SAP is making available BAPIs for most of the functionalities, someone should first look out for BAPI if it is not available then go for BDC."
So, does this classify BAPIs as both an interface and a conversion tool in RICEF?
BAPI stands for Business API or Business Application Programming Interface. It is a way for custom code to interface with the SAP system. So, you can (should) use them any time you need to read data from the SAP system or need to make updates to it. They are not limited in their use for any of the RICEF (Report, Interface, Conversion, Enhancement, Form) objects, there are scenarios for any of these objects to use BAPI's.