Predominantly a gasoline powered, bladed machine used in the process of cutting grass.
This category covers a large amount of different types: riding, self-propelled, walk behind, etc. Many different manufacturers make these: Honda, Craftsman, Cub, John Deer, etc.
While there are a plethora of engine manufacturers out there, the predominant engine used in mowers in the US are Briggs & Stratton branded engines, though Honda has a good following as well. Engine sizes can range from small (3hp and below) up to large (20hp+). This is all dependent upon the needs of the mower and the design the factory has put forth.