What is social policy and how is it related to other public policy?
Public policy is usually divided first into foreign and domestic policy, where domestic policy involves your own country and foreign policy involves your relationship with other countries.
Then, domestic policy is subdivided into social policy and economic policy, where economic policy is about inflation, unemployment, taxes, and market regulation, while social policy is about everything else, including women's rights, racial equality, environmental regulations, and a variety of other issues.
Social policy is sort of a catchall term that deals with any issue of public policy that involves the general welfare of a society but doesn't have a clear connection with macroeconomics.
In practice these distinctions are often not clear-cut. Some would consider trade agreements to be economic policy, others to be an aspect of foreign policy. Social insurance and public healthcare systems (such as Social Security and Medicare) could be considered either economic or social policy. Often a policy intended to achieve some social goal has an economic impact, and economic policy often has social effects as well, especially in societies with high levels of inequality that are closely linked to categories such as race and gender.
Still, it can be a useful distinction. Social issues such as abortion and same-sex marriage are usually more closely tied to questions of morality and religious opinions, where the methods are not complicated (do you let people of the same sex get married or not?) but the disagreements are fundamental, involving different visions of what society should be like. Economic issues such as tax rates and inflation targets are often more complex and technocratic, where the goals (high economic growth, low unemployment) are largely agreed-upon, but the methods of getting there require advanced expertise to determine.