Tethered
From AmtWiki
Tethered
Vulnerability of some Monsters
Description from the Dor Un Avathar
Creatures with this distinction are secured to a central location with a length of sturdy rope and may not move beyond the radius specified in the text. For larger groups, or places where rope may not be practical, safe or available, the tethered range should be marked on the ground with ribbon, chalk powder or similarly easy-to-see media.