Social Darwinism is the study and implementation of various pseudoscientific theories and societal practices that purport to apply biological concepts of natural selection and survival of the fittest to sociology, economics and politics. Social Darwinists believe that the strong should see their wealth and power increase, while the weak should see their wealth and power decrease. Social Darwinist definitions of the strong and the weak vary, and differ on the precise mechanisms that reward strength and punish weakness. Many such views stress competition between individuals in laissez-faire capitalism, while others, emphasizing struggle between national or racial groups, support eugenics, racism, imperialism and/or fascism.

"Survival of the fittest" is a phrase that originated from Darwinian evolutionary theory as a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success. In Darwinian terms, the phrase is best understood as "[s]urvival of the form that in successive generations will leave most copies of itself."