What are the definitions of social stratification and poverty?

As the saying goes, some people have more than others. However, we now see that some people have way more than others! (a) What are the definitions of social stratification and poverty? (b) What are the arguments for the justification of inequality? The fact that inequality is higher and has risen in the United States than in other countries suggest that something different is going on in the United States. (c) What are the reasons for the widening gap, and the rise in inequality, in the United States?