What is "SAP on Oracle" OK, total newb question.

What is "SAP on Oracle", exactly.  This link is talking about how SAP can run on Oracle (I think).

I'm not understanding how this is working.

My understanding:


SAP is a company that provides ERP
Oracle is a database system.


I thought they were competitors!  So, is SAP on Oracle running the ERP system on Oracle?  What is running here and what would a DBA be supporting in this scenario?  (Or would this even be DBA territory?)

I'm asking because I've applied for a job that prefers "SAP" experience and I ran into this "SAP on Oracle" in my googling.
SAP AG (Often just called SAP) is a company which has a product called SAP ERP (Enterprise Resource Planning).  Since Oracle also makes ERP software they are indeed competitors.  In fact they are the top two ERP vendors.  

SAP can be used with quite a few different database systems, but according to one source I found Oracle is dominant comprising around 80% of SAP systems.  Oracle recently won a law suit against SAP for intellectual-property theft. (http://news.cnet.com/8301-1001_3-20029601-92.html#ixzz1CWy7UiKR) 

Here is some SAP on Oracle documentation.

It does seem like a strange scenario for a product to depend so heavily on a competitors product, but it is not unheard of.  To some extent this pattern exists for Oracle with their database product running on Microsoft Windows servers.