There seems to be some confusion about the various aspects of this business, as far as drivers are concerned. I hope this can clear up some of the confusion.
Company Driver - This is someone who drives a truck for a carrier.
Lease Operator - A driver who leases a truck from the carrier to whom he is leased. The Lease Operator has most of the same responsibilities of an Owner Operator, but doesn't own the truck. Some carriers will never allow the Lease Operator to buy out his lease. Most Lease Operators must leave their truck should they decide to leave the carrier to whom the truck is leased.
Owner Operator - This individual owns his own truck but leases to a motor carrier. He is responsible for all maintenance and operating costs. He is free to leave the carrier to whom he is leased at any time and can take his truck with him. These people usually run a fixed rate for the miles they run (mileage pay) or percentage. The percentage owner operator usually has more freedom or say as to what loads he takes and where he runs.
Fleet Owner - This individual owns 2 or more trucks and leases them to a motor carrier in much the same fashion as an owner operator. He has his own drivers who work for him, not the carrier.
Motor Carrier - A motor carrier is someone who has their own authority. This can be a single truck operation or several thousand. The process is the same for every one, regardless of size. A motor carrier is assigned a MC number and also a DOT number. He is responsible for all insurance, filing all permits and fuel taxes. He can also lease on owner operators under his authority. There are very specific guidelines to leasing on owner operators. Some people confuse being an owner operator with being a motor carrier due to the size of the company. A case could probably be made that the single truck carrier is also an owner operator if the owner drives the truck, but the term owner operator usually applies to those who own their equipment and lease to a motor carrier.