Horizontal integration is the operation by a single owning entity of a range of similar businesses in the same industry, usually after a takeover and sometimes as a merger. The concept is based on using the multiple market presences of the original businesses and penetration of the different markets of each business. The 'integration' element involves the businesses operating collectively as a single business for the owner.
Horizontal integration is essentially a merger of business interests. This is a common term in takeovers, when a business buys or merges with a competing business.
The process of horizontal integration is based on efficiencies and deriving maximum benefits from the merger.