The term "Western world" can mean a number of different things, but generally it refers to countries in Europe and North America. Some widen the term to include Latin America and other countries around the world that descended from European culture. It is often used interchangeably with "first world" nations.
Originally, the term had a specifically geographic meaning, defining countries in Europe in relation to the Eastern world, which consisted of the Middle East and Asia. Over time, however, the term began to refer more to the cultural aspect of civilization rather than its geographic layout. Countries of the West tend to have cultural, economic and sometimes political similarities.