A video on the Helicopter Association International (HAI) website defines the hazard for helicopters, but also fixed-wing aircraft. You can see it here. For fixed wing pilots flying on instrument flight plans in marginal weather, the defined routes will keep you out of danger. But every so often, a pilot will try to become creative with an IFR procedure, for example, flying an instrument approach to one airport and scudrunning on to another nearby field. Though cloud layers may be safely above terrain levels, there could be high towers with support cables in between. They can be lethal.