The Definition of Tourism varies source by source, person by person. There is no consensus concerning the definition of tourism. Nearly every each institution define "Tourism" differently. But When it comes to explain it with the basic terms, we can sum it up as follows;
“Tourism is the practice of travelling for pleasure or the business of offering information, accommodations, transportation and other services to tourists.”

tour·ism [toor-iz-uhm] (noun)

1. the activity or practice of touring, especially for pleasure.

2. the business or industry of providing information, accommodations, transportation, and other services to tourists.

3. the promotion of tourist travel, especially for commercial purposes.

Source: Dictionary.com

The Meaning of Tourism

"the sum of the phenomena and relationships arising from the travel and stay of non-residents, insofar as they do not lead to permanent residence and are not connected with any earning activity." - Hunziker and Krapf

In 1994, the United Nations identified three forms of tourism in its Recommendations on Tourism Statistics:

The terms tourism and travel are sometimes used interchangeably. In this context, travel has a similar definition to tourism, but implies a more purposeful journey. The terms tourism and tourist are sometimes used pejoratively, to imply a shallow interest in the cultures or locations visited by tourists.

Tourism is different from travel. In order for tourism to happen, there must be a displacement: an individual has to travel, using any type of means of transportation (he might even travel on foot: nowadays, it is often the case for poorer societies, and happens even in more developed ones, and concerns pilgrims, hikers …). But all travel is not tourism.

Three criteria are used simultaneously in order to characterize a trip as belonging to tourism. The displacement must be such that;