Rychetnik et al. (2003) define evidence-based public health as "a public health endeavour in which there is an informed, explicit, and judicious use of evidence that has been derived from any variety of science and social science research and evaluation methods" (p. 538).
This definition is derived from the definition of evidence-based medicine by Sackett et al. (1996): "the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients" (p. 71).
References:
Rychetnik, L., Hawe, P., Waters, E., Barrat, A., Frommer, M. (2004). A glossary of evidence based public health. Journal of Epidemiology and Community Health, 58, 538-545. doi:10.1136/jech.2003.011585
Sackett, D. L., Rosenberg, W. M., Gray, J. A., Haynes, R. B., Richardson, W. S., (1996). Evidence based medicine: what it is and what it isn't. British Medical Journal, 312, 71-72.