EBM is "the conscientious, explicit and judicious use of current best evidence in making decisions about the care of the individual patient. It means integrating individual clinical expertise with the best available external clinical evidence from systematic research."
Sackett, D., Rosenberg, W., Gray, J., Haynes, R., & Richardson, W. (1996, January 13). Evidence based medicine: What it is and what it isn't. BMJ, 312(7023), 71-72. Retrieved from http://www.bmj.com
Or another way of defining it...
EBM is "the use of mathematical estimates of the risk of benefit and harm, derived from high-quality research on population samples, to inform clinical decision making in the diagnosis, investigation or management of individual patients."
Sackett, D. and Haynes, B. (1995). On the need for evidence-based medicine. Evidence Based Medicine, 1, 4-5. Retrieved from http://ebm.bmj.com/