Less-than-truckload: freight too small to fill a trailer is combined with other shippers' loads and routed through regional terminals, rather than moving direct point-to-point.
Less-than-truckload freight moves through a hub-and-spoke network instead of point-to-point: a shipment too small to fill a trailer rides with other shippers' freight to a regional terminal, gets unloaded and resorted alongside freight headed the same direction, and continues on a different trailer. That extra handling is why LTL freight is priced and classified differently from full truckload freight, and why it typically takes longer and sees more handling than a truckload that never leaves the trailer it started in.