6×6 in the context of Drivetrain

A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most commonly, the term is used to describe a farm vehicle that provides the power and traction to mechanize agricultural tasks, especially (and originally) tillage, and now many more. Agricultural implements may be towed behind or mounted on the tractor, and the tractor may also provide a source of power if the implement is mechanised.

Mechanized infantry are infantry units equipped with armored personnel carriers (APCs) or infantry fighting vehicles (IFVs) for transport and combat (see also armoured corps).

As defined by the United States Army, mechanized infantry is distinguished from motorized infantry in that its vehicles provide a degree of armor protection and armament for use in combat, whereas motorized infantry are provided with "soft-skinned" wheeled vehicles for transportation only. Most APCs and IFVs are fully tracked or are all-wheel drive vehicles (6×6 or 8×8), for mobility across rough ground. Some militaries distinguish between mechanized and armored (or armoured) infantry, designating troops carried by APCs as mechanized and those in IFVs as armored.

A ballast tractor is a specially weighted tractor unit of a heavy hauler combination. It is designed to utilize a drawbar to pull or push heavy or exceptionally large trailer loads which are loaded in a hydraulic modular trailer. When feasible, lowboy-style semi-trailers are used to minimize the height of a load's center of mass. Typical drivetrains are 6×4 and 6×6, but 8×6 and 8×8 are also available. Typical ballast tractor loads include oil rig modules, bridge sections, buildings, ship sections, and industrial machinery such as generators and turbines.

Only a handful of manufacturers produce dedicated ballast tractors. Extra-heavy-duty chassis versions of mass-production tractor units are fitted with drawbar hitches and a separate ballast box as an alternative. These units are classified as N3 Category of large goods vehicle. Ballast tractors can be traced back to the 1940s when heavy haulers from the UK started employing purpose-built Scammell Showtracs, a short wheelbase 4×2 ballast tractor.

A tractor unit, also known as a truck unit, lorry unit, power unit, prime mover, ten-wheeler, semi-tractor, semi-truck, semi-lorry, big rig tractor, big rig truck or big rig lorry or simply a tractor, truck, lorry, semi, big rig or rig, is a characteristically heavy-duty towing engine that provides motive power for hauling a towed or trailered load. The largest such vehicles are similar to locomotives. These fall into two categories: heavy- and medium-duty military and commercial rear-wheel-drive semi-tractors used for hauling semi-trailers, and very heavy-duty typically off-road-capable, often 6×6, military and commercial tractor units, including ballast tractors.

It should not be confused with a tractor-trailer which is a combination of a tractor unit and semi-trailer, whereas a tractor unit describes only the tractor portion.

An all-wheel drive vehicle (AWD vehicle) is one with a powertrain capable of providing power to all its wheels, whether full-time or on-demand.