“In survival analysis, the hazard ratio (HR) is the ratio of the hazard rates corresponding to the conditions described by two levels of an explanatory variable. For example, in a drug study, the treated population may die at twice the rate per unit time as the control population. The hazard ratio would be 2, indicating higher hazard of death from the treatment. ..” (1)
(1) Wikipedia contributors, 2016. Hazard ratio. Wikipedia, The Free Encyclopedia. Available at: https://en.wikipedia.org/w/index.php?title=Hazard_ratio&oldid=731433663 [Accessed August 8, 2016].