Definitions of Developed country on the Web:

• The term developed country is used to describe countries that have a high level of development according to some criteria. ...
  en.wikipedia.org/wiki/Developed_country

• A country whose per capita income is high by world standards.
  www-personal.umich.edu/~alandear/glossary/d.html

• a country with a relatively high per capita income, where most people have a higher standard of living with access to more goods and services than ...
  www.pbs.org/strangedays/glossary/D.html

• An area of the world that is technologically advanced, highly urbanized and wealthy and has generally evolved through both economic and ...
  www.cbsd.org/holicong/jendorman/PA_socialstudies_standards_vocabulary.htm