Any person that owns and operates their own equipment is, by definition, an owner/operator. It matters not if you have a lease agreement with a carrier, have an employment agreement with a carrier, operate under the authority of a freight broker, or have your own authority and find your own customers, you're an owner/operator if you own and operate your own truck.
Independent Contractor (IC) is mainly an IRS classification used to separate an employee's tax status from that of the Independent Contractor. Expedite carriers that lease Owner/Operators(O/O)for the carriage of their freight, classify us a Indepentent Contractors and loosely adhere to the IRS's definition of IC so that they can avoid the burden of employee Federal, state and local withholding taxes, FICA taxes, workers compensation premiums, unemployment taxes and the payment of any benefit packages offered to employees.
Most expedite carriers have lease agreements with O/Os to obviate the procurement of their own trucks and drivers. In this manner, they can accept or reject any O/O who wishes to agree to the terms of their lease agreement. These terms usually, if not always, include standards of operations to which both parties agree. At any point in time that one or the other party does not agree with the other, the lease agreement may be terminated.
As Joebob indicated, there is no small expense for the O/O to own one or more trucks. Conversely, there is no small expense for a carrier to recruit, lease, train/orient, license/permit and maintain O/Os and their truck. In addition, they must find, schmooze, bill and satisfy their customers to get the freight for us. In exchange for their role in the lease greement, the O/O is expected to maintain a reasonable percentage of availability to haul the freight they find and to accept a reasonablle percentage of the freight offered.
As I reread what I've just written, I know I sound somewhat like a company stooge, but let's be realistic...there is no free ride in life or in expediting. Even an owner with his own authority, who gets all loads from load boards, rejects way more than 50% of the loads offered on the board. That same owner has no real negotiating power with any of the brokers used and may sit longer than an expediter if only taking the premium paying loads.
I choose to be an IC with an O/O lease to a carrier because it eliminates the burden of authority maintaining, permit getting, load finding, customer billing and payment worrying that is enjoyed by those without lease agreements.