Western world
Western world has meant various things at various times. In the earliest history of Europe, it referred to Ancient Greece and the Aegean. During the Roman Empire, it meant the Western Roman Empire (covering the area from Croatia to Britain). At other times, it has meant Western Europe or Europe or Christendom. During and after the Cold War, it sometimes meant the democratic countries or those allied with the various NATO powers.

In this day and age, it often refers to the places that have a European cultural heritage, called Western civilization. This European heritage itself is a combination of Judeo-Christian ethic, classical Greco-Roman thinking and the cultural practices of the "barbarian" peoples of Northern Europe. Under the strictest definition, it would be the United States, Canada, Western Europe, Australia, and New Zealand.
At its widest medieval definition, it includes the following 36 countries:
Andorra
Australia
Austria
Belgium
Canada
Croatia
Czech Republic
Denmark
Estonia
Finland
France
Germany
Hungary
Iceland
Ireland
Italy
Latvia
Liechtenstein
Lithuania
Luxembourg
Monaco
Netherlands
New Zealand
Norway
Portugal
Poland
San Marino
Slovakia
Slovenia
Spain
Sweden
Switzerland
United Kingdom
United States
Vatican City