What does this attribute in AngularJS mean?

I saw a ui-select2 attribute in some AngularJS code:

<select ui-select2 name="..." ng-model="..." ng-options="...">

What does it mean?

The ui-select2 directive is not actually a part of AngularJS, it is from AngularUI :

http://angular-ui.github.com/#directives-select2.

As you can see in the link, the ui-select2 directive is just a wrapper for integrating the Select2 jQuery plugin with AngularJS. Basically, an enhanced combo box.