Webtrends Analytics Query Parameters Reference, October 2013
This parameter contains the value of the DCSID that generated the hit. The Standard Analysis Engine, Express Analysis Engine, and Event Database Loader pass the DCSID as value of for this parameter.
This parameter becomes most useful when tracking multiple DCSIDs in SmartSource files from multiple sites. In this case, you can use this parameter to segment your report data by site. For example, you can use this parameter as a dimension in a custom report to report on activity for each site.