The Southern strategy (n.) is a strategy partly grounded in a spiritual defense of segregation, which held that the Bible prohibited the integration of blacks and whites.
Southern strategy (n.) is the Republican strategy of winning white Southern voters, partly through appeals to racial resentment.
The Southern strategy (n.) is an intentional maneuver on the part of the Republican Party to win elections, and Goldwater, with his ability to appeal to racist sentiments in the South, was seemingly the only candidate who could deliver enough Southern votes to ensure a Republican victory.
The Southern strategy (n.) is older than generally thought -- it was born not in the 1960s but in the 1950s Southwest, and was in fact explicitly racial in motivation and application.