Economic development can be indicated by various factors and metrics. Some common indicators of economic development discussed in the document include:
1. GNP per capita - The total GNP of a country divided by its population, as a measure of average income.
2. Social indicators - Factors like health, education, and living standards that measure quality of life beyond just income levels.
3. HDI - The Human Development Index, a composite index used by the UN to measure development based on health, education, and income indicators.