In addition to all the regular confusion around SAP issues might also stem form the fact that SAP used to have their own DBMS ..
It used to be called Adabas (marketed originally by Nixdorf and then by Software AG) and was a quite popular DBMS for smaller SAP (the ERP solution) installations in Germany. At some point (AFAIK around 2000) SAP started to co-develop/support/take over Adabas and marketed it as SAP DB and later MaxDB under commercial and open-source licenses. There also was/is some agreement with MySQL.
But when people talk about SAP, they usually refer to the ERP solution as the other posters have noted.