Teststand is a Test Executive that runs on top of such things like LabVIEW, CVI, DLL's, ActiveX etc.. If you could imagine a test sequence that has many steps in it. Each step could be written in LabVIEW or CVI or a DLL or ActiveX. Where Teststand comes in is that it controls these steps and allows you to make descisions based on these step results. In addition it has built in database connectivity, report generation and many other features I can't begin to explain. But the basic concept is that it is a Test Executive. You can find more info at:
http://sine.ni.com/apps/we/nioc.vp?cid=1459〈=US