Anyone know what the Stealthy trait on the Marru is?

By laak, in Only War Rules Questions

Marru (Minion)
WS BS S T Ag Int Per WP Fel
40 01 45 34 39 15 42 23 15
Movement: 8/16/24/48 Wounds: 12
Armour: None. Total TB: 3
Skills: Awareness (Per), Dodge (Ag), Stealth (Ag).
Talents: Catfall, Heightened Senses (Hearing), Leap Up.
Traits: Bestial, Dark Sight, Deadly Natural Weapons, Flyer
(8), Quadruped, Size (5), Stealthy , Terrain Master, Unnatural
Perception (2).
Weapons: Fangs and claws (Melee; 1d10+4 R; Pen 0).

right there page 140 of only war Hammer.

i can't find anything on the trait. any ideas?