What does LTL mean for truck drivers?

Less-Than-Truckload. To make a complete truckload, companies will combine partial shipments onto a single truck. Some companies specialise exclusively in LTL shipments - FedEx Freight and FedEx National LTL, UPS Freight (formerly Overnite), Estes, Con-Way Freight, Yellow-Roadway Corporation, ABF, etc., but all companies will do LTL shipments, if they can combine partials to make complete truckloads.