Definition of 'First World'
1. A country that was aligned with the West and opposed to the Soviet Union during the Cold War. Since the collapse of the Soviet Union in 1991, this use of First World has largely gone away.
2. A country characterized by political stability, democracy, rule of law, a capitalist economy, economic stability and a high standard of living. Various definitions have been used for First World nations, including GDP, GNP and literacy rates. The Human Development Index is also a good indicator in determining First World countries.
Investopedia explains 'First World'
First-world countries have stable currencies and robust financial markets, making them attractive to investors from all over the world. Examples of first-world countries include the United States, Canada, Australia, New Zealand, Japan and the Western European countries. First-world countries are in the minority; most countries are classified as second- or third-world.