SQL Server Security Option w/ Intermediate Check Option? What does that mean?

This afternoon I was reviewing the security for a user in my SQL Server, in SQL Server Management Studio. I opened the Database User's Properties dialog, and went to the Securables section.

As I was cycling through t开发者_如何学编程he tables and stored procedures that this particular user had access to, I noticed that one of the data tables had the the Update option checked in an intermediate state. What does that mean? You can either update a row, or you can't. There is no in-between. I've included an image for reference. I would just fully check this option and save it but I'd rather not screw with the DB if this serves a worthwhile purpose.

I believe that means that that permission has been inherited and wasn't explicitly set for that user.

The GRANT statement can assign permissions to a group or role that can be inherited by database users.

http://msdn.microsoft.com/en-us/library/bb669084.aspx

I'm trying to find something that specifically spells out that's what the checkbox looks like in the above situation.