A strap is a heavy-duty tie-down, typically made of tough vinyl or polyester webbing with a ratchet, used to lash cargo firmly to a trailer. Properly tensioned straps keep a load from sliding, tipping, or falling off while the truck is moving.
They’re central to flatbed and step deck work, where open freight has to be secured against the road. How many straps, and where, depends on the weight and shape of the load — and cargo securement is itself a regulated safety requirement.