Set feature on codechef

what is set feature on codechef which appears on top of profile in the right side of fb n editing option icon?
It makes a list of some users. I want to know what exactly it is and what is its purpose…?

When u open the Rankings of a Contest. There u can see 4 Options to select from [“institution”,“Institution Type”,“Set”,“Country”]. There u can select some set of People that u have created and check their rankings only.