A developing country normally has comparatively low level of affluence and more unemployment rate. In developing countries, there is low per capita income, poverty, less education level and low capital formation. Such countries are fighting to get these things, but might not have reached them. These countries are usually suffered from war, disease, poverty, natural disasters, etc.
The developed/advanced countries have developed economies. They have technological improvements, excellent roads, a steady government etc. This level of economic development usually translates into a High GDP per capita (average income), Good education, Good health-care, and Death & birth rate are almost the same.