There are creatures whose physical bodies have long since rotted away, if indeed they ever existed. Such beings are immune to normal weapons – only magic can harm them.
Source: Warhammer Fantasy: 8th Edition
Ethereal creatures treat all terrain as open terrain for the purposes of movement. They may not finish their movement inside impassable terrain – though they can pass through obstructions of this kind, they cannot linger. They are also never slowed by any special rule, spell or item that would otherwise reduce their movement or stop them from moving completely.
The close combat attacks of Ethereal creatures are magical. Conversely, Ethereal creatures can only be wounded by spells, magical attacks and magic weapons or effects. This is not to say that Ethereal creatures cannot be beaten in close combat by mundane troops, because combat results are not wholly dependent upon casualties.
Ethereal creatures block line of sight normally and cannot see through anything that would block the line of sight of normal units.
Characters that are not themselves Ethereal are not permitted to join units that are (even if they become temporarily Ethereal for some reason).