Different persons can have different developmental goals. What may be development for one may not be development for the other. It may even be destructive for the other.
Besides seeking more income, people also seek things like equal treatment, freedom, security, and respect of others. For development, people look at a mix of goals. The developmental goals that people have are not only about better income but also about other important things in life.
For comparing countries, their income is considered to be one of the most important attributes. Countries with higher income are more developed than others with less income. The average income is the total income of the country divided by its total population. The average income is also called per capita income.