The btstackserver.exe process is used by your computer to communicate with bluetooth devices (e.g. bluetooth enabled mobile phones or handheld computers etc) If you connect to your computer using bluetooth devices you should leave this process running. If you do not, it can be safely terminated.
btstackserver.exe is flagged as a system process and does not appear to be a security risk. However, removing Bluetooth Stack may adversly impact your system.
The Process Server database currently registers btstackserver.exe to WidComm.