Get Craft UserGroup by ID in Plugin
You'll want to go through Craft's service layer to get things like that.

There is a UserGroupsService, which has all sorts of handy methods for retrieving UserGroups like getGroupById() and getGroupByHandle().

You can invoke these from your plugin like:

$userGroup = craft()-&gt;usergroups-&gt;getGroupById(3);
$groupName = $userGroup-&gt;name;


Note that these will return a UserGroupModel populated with your UserGroup information.