What is horizontal integration?
horizontal integration is Merging of two or more firms at the same level of production in some formal, legal relationship. In hospital networks, this may refer to the grouping of several hospitals, the grouping of outpatient clinics with the hospital, or a geographic network of various health care services. Integrated systems seek to integrate both vertically with some organizations and horizontally with others.
source: A GLOSSARY OF TERMS FOR COMMUNITY HEALTH CARE AND SERVICES FOR OLDER PERSONS. World Health Organization, 2004.