The creature is immobilized.
Maintaining this condition on the creature occupies whatever appendage, object, or effect the grabber used to initiate the grab.
This condition ends immediately on the creature if the grabber is subjected to an effect that prevents it from taking actions, or if the creature ends up outside the range of the grabbing power or effect.
A grabbed creature can take the escape action to try to get away. Other common tactics for escaping a grab are to teleport away or to be pulled, pushed, or slid out of the grabber’s reach. Using forced movement on the grabber can also end a grab, as long as the movement results in the grabbed creature being out of the grabbing effect’s range.
While a creature is grabbed, the grabber can try to move it (see “Moving a Grabbed Target”.
Published in Monster Manual 2, page(s) 217, Rules Compendium, page(s) 231, Monster Vault: Threats to the Nentir Vale, page(s) 123.