If the defender has suitable models, then they may set up razorwire. Razorwire comes in 6" long sections. If the defender has obstacles, then they get 1D3+3 6" long sections of razorwire to deploy at the start of the game.
Razorwire counts as difficult ground for all infantry, cavalry and bikes. Vehicles can drive over razorwire with no effect. Skimmers and jetbikes are not affected by razorwire, neither are jump pack troops.