The development of a country is measured with statistical indexes such as income per capita (per person) (gross domestic product), life expectancy, the rate of literacy, et cetera. The UN has developed the Human Development Index (HDI), a compound indicator of the above statistics, to gauge the level of human development for countries where data is available.
Developing countries are in general countries which have not achieved a significant degree of industrialization relative to their populations, and which have, in most cases a medium to low standard of living. There is a strong correlation between low income and high population growth.
The terms utilized when discussing developing countries refer to the intent and to the constructs of those who utilize these terms. Other terms sometimes used are less developed countries (LDCs), least economically developed countries (LEDCs), "underdeveloped nations" or Third World nations, and "non-industrialized nations". Conversely, developed countries, most economically developed countries (MEDCs), First World nations and "industrialized nations" are the opposite end of the spectrum.
To moderate the euphemistic aspect of the word developing, international organizations have started to use the term Less economically developed country (LEDCs) for the poorest nations which can in no sense be regarded as developing. That is, LEDCs are the poorest subset of LDCs. This may moderate against a belief that the standard of living across the entire developing world is the same.
The concept of the developing nation is found, under one term or another, in numerous theoretical systems having diverse orientations — for example, theories of decolonization, liberation theology, Marxism, anti-imperialism, and political economy.