Immobile
Immobile beasts cannot travel under their own power. They may still attack adjacent tiles.
Some like rocks can be rolled around.
Creatures with this trait: Anvil, Cactus, Cage, Cauldron, Clam, Jellyfish, Leech, Palm tree, Pot, Rock, Table, Throne, Toadstool, Tree, Urchin
The same tag on items means something else.