RDO (Remote Data Objects) is an application program interface (API) from Microsoft that lets programmers writing Windows applications get access to and from both Microsoft and other database providers. In turn, RDO statements in a program use Microsoft's lower-layer Data Access Objects (DAO) for actual access to the database. Database providers write to the DAO interface.
RDO has evolved into ActiveX Data Objects (ADO) which is now the program interface Microsoft recommends for new programs. ADO also provides access to nonrelational databases and is somewhat easier to use.