The Graduate Studies (typically just Grad Studies) oversees academic and administrative services for academic graduate students and postdoctoral scholars. They're somewhat akin to the Colleges for undergrads. What they do oversee is:

The department is led by Prasant Mohapatra, Vice Provost of Graduate Education and Dean of Graduate Studies. The Graduate Studies offices are currently in Mrak Hall, though the staff is slated to move into Walker Hall by 2020.

Grad Studies Website