International tourism refers to tourism that crosses national borders. Globalization has made tourism a popular global leisure activity. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes". The World Health Organization (WHO) estimates that up to 500,000 people are in flight at any one time.
As a result of the late-2000s recession, international travel demand suffered a strong slowdown from the second half of 2008 through the end of 2009. This negative trend intensified during 2009, exacerbated in some countries due to the outbreak of the H1N1 influenza virus, resulting in a worldwide decline of 4.2% in 2009 to 880 million international tourists arrivals, and a 5.7% decline in international tourism receipts. In 2010, international tourism reached US$919B, growing 6.5% over 2009, corresponding to an increase in real terms of 4.7%. In 2010, there were over 940 million international tourist arrivals worldwide.
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