Business Keys

Business Key columns identify one or more columns that the SCD component can use to determine how Existing Dimension rows get matched up to Source Systemrows, in order to determine if any changes have occurred in the source system.

http://support.sas.com/documentation/cdl/en/etlug/62233/HTML/default/n03673ddo0y2twn114ephiuc8s5o.htm

Read about Slowly Changing Dimensions: 

http://copypastenet.blogspot.com/2011/03/slowly-changing-dimensions.html