From the WHO:
The social determinants of health are the conditions in which people are born, grow, live, work and age. These circumstances are shaped by the distribution of money, power and resources at global, national and local levels. The social determinants of health are mostly responsible for health inequities - the unfair and avoidable differences in health status seen within and between countries.
The social determinants of health play a much larger role in shaping population health outcomes than genetics, healthcare, or individual lifestyle choices. Read more on this topic here from the King's Fund.