A tractor (from latin trahere) is a device intended for drawing, towing or pulling something which cannot propel itself.
Most commonly the word is used to describe a vehicle intended for such a task on some other vehicle or object.
The most common use of the term tractor is for the vehicles used on farms. The classic farm tractor is a simple open vehicle with two very large driving wheels on an axle below and slightly behind a single seat and the engine in front of the driver with two steerable wheels below the engine compartment.
The farm tractor is used for pulling agricultural machinery or trailers, ploughing, harrowing and similar tasks. Modern farm tractors can be quite large with eight driven wheels, four on the front axle and four on the back axle, and articulated steering. Variations of the classic style are used for smaller farm tasks, mowing grass, and landscaping.
Most tractors have a means to transfer the engine's power to another machine such as a baler or reaper. Early tractors used belts wrapped around pulleys to power stationary equipment. Modern tractors use a PTO (power take-off) to provide rotary power to machinary that may be stationary or pulled. Almost all modern tractors can also provide hydraulic and electrical power.
Most equipment attached to the rear of the tractor use the three-point hitch (invented by Harry Ferguson) which has been a standard since the 1960's.
A common attachment for the front of a tractor is a front-loader or loader and tractors with this attachment are often called a loader or front-loader. This consists of two hydraulic powered arms on either side of the front engine compartment and a tilting impliment. This is usually a wide open box called a bucket but other common attachments are a pallet fork and a bale grappler.
Another common use of the term tractor is to denote a heavy engineering equipment vehicle which can be attached with different engineering tools such as dozer blade, front-loader|bucket, hoe, ripper etc. See also the terms tracked-type tractor, crawler and bulldozer.
The most common variation of the classic farm tractor is the loader-backhoe. Although derived from the classic farm tractor it is almost never called a tractor, is not generally used for towing and usually does not have a PTO. An articulated backhoe arm is permenantly attached to the rear of the loader-backhoe. The front of the tractor has a loader.
A less-well-used term is used to describe road tractors, which are heavy-duty vehicles with large engines and several axles. These tractors are designed to pull long road trailers, most often for the transport of freight of some kind over a significant distance (See Semi-trailer).
Of non-vehicles, a tractor is a part of printer that pulls the paper inside and pushes it outside of the printer.