MOSS 2007 had a feature called Business Data Catalog. When SharePoint 2010 came out, this feature was introduced as Business Connectivity Services.
The common belief is that BCS is the new version of BDC, and that in the new version the name was changed from BDC to BCS. According to this, there is no reason to use the term BDC in the context of SharePoint 2010.
This is not exactly correct.
BDC was and still the infrastructure that allows SharePoint to connect to other systems. It has the concept of metadata and descriptors, and is still present in 2010 under the name “Business Data Connectivity”. BCS is based on BDC and is what makes all the advanced connectivity scenarios possible (such as integration with Office, ECT,…).
In the bottom-line, the terms BDC and BCS is used interchangeably, so you should too. But you don’t have to be angry if you see BDC in the same sentence with SharePoint 2010 :)
Here are some supporting quotes from MSDN:
“Business Data Connectivity (BDC) service is the new version of the Business Data Catalog that was provided in Microsoft Office SharePoint Server 2007”
“Business Data Connectivity (BDC) service succeeds the Business Data Catalog that was provided in Microsoft Office SharePoint Server 2007”
“BDC is the foundation of Business Connectivity Services”
“Business Data Connectivity (BDC) service in Microsoft Business Connectivity Services (BCS) is the underlying framework in the Microsoft SharePoint Foundation 2010 platform on which Business Connectivity Services is built”