List of first world countries

Photocopied from a 2004 World Atlas

This seems to be missing quite a bit, countries like Korea, Taiwan, Argentina, Scotland, Czech Rep. etc...What is the exact definition of 1st world, how come it changes so much?

1st World:

Andorra
Australia
Austria
Belgium
Canada
Cyprus
Denmark
Finland
France
Germany
Greece
Iceland
Ireland
Israel
Italy
Japan
Liechtenstein
Luxembourg
Malta
Monaco
Netherlands
New Zealand
Norway
Portugal
Spain
Sweden
Switzerland
Turkey
United Kingdom
United States
Vatican city>