A lawn mower is a device utilizing one or more revolving blades to cut a grass surface to an even height. The height of the cut grass may be fixed by the design of the mower but generally is adjustable by the operator, typically by a single master lever or by a mechanism on each of the machine's wheels. The blades may be powered by manual force, with wheels mechanically connected to the cutting blades so that the blades spin when the mower is pushed forward, or the machine may have a battery-powered or plug-in electric motor. The most common self-contained power source for lawn mowers is a small internal combustion engine. Smaller mowers often lack any form of self-propulsion, requiring human power to move over a surface; "walk-behind" mowers are self-propelled, requiring a human only to walk behind and guide them. Larger lawn mowers are usually either self-propelled "walk-behind" types or, more often, are "ride-on" mowers that the operator can sit on and control. A robotic lawn mower is designed to operate either entirely on its own or less commonly by an operator on a remote control.

A lawn is an area of soil-covered land planted with grasses and other durable plants such as clover which are maintained at a short height with a lawn mower and used for aesthetic and recreational purposes—it is also commonly referred to as part of a garden. Lawns are usually composed only of grass species, subject to weed and pest control, maintained in a green color, and are regularly mowed to ensure an acceptable length. Lawns are used around houses, apartments, commercial buildings and offices. Many city parks also have large lawn areas. In recreational contexts, the specialised names turf, pitch, field or green may be used, depending on the sport and the continent.