The following is summarized from http://en.wikipedia.org/wiki/Horizontal_integration. This is a technical phrase from microeconomics and strategic management, describing a type of ownership and control. A less technical term for it is "merger." Horizontal integration occurs when a firm in the same industry and in the same stage of production is taken over or merged with another firm which is in the same industry and in the same stage of production. For example, a car manufacturer merging with another car manufacturer. In order to be an example of horizontal integration, it is important that both companies are in the same stage of production and also in the same industry.