what does installd do in privacy setting? there is a installd icon in the setting->accessibility->privacy. it can be seen in the screenshot 

Any ideas what it is for?
I've had this question as well and finally went digging.  This information is stored in the OS X Privacy database.  This db can be accessed with the command-line tool tccutil, but the only ("supported") option is reset.  That is of course not very useful here. I found someone at this page who wrote a short python utility to edit this database.  Examining the code, the db is located at /Library/Application Support/com.apple.TCC/TCC.db (you will need sudo access for this).  It is a SQLite db.  There are entries in there for /System/Library/PrivateFrameworks/PackageKit.framework/Resources/installd which is almost certainly the installd referenced in the preference pane.  This is the daemon which occasionally checks for software updates. Since it is Apple code, I am inclined to trust it.