Because of its reliance on primary, secondary, and tertiary levels of production and service, as well as the fact that it is so intimately intertwined into the fabric of life economically, socio-culturally, and environmentally, tourism has proven difficult to define (Fennell, 2015).

 In a 1991 issue of The Economist, the difficulty is mirrored:

There is no universally agreed definition of the [tourist] business, and every attempt to define it risks overestimating or underestimating economic activity. At its most basic level, the industry transports people from one location to another (and back), as well as providing shelter and food for them while they are away. But that won’t go you very far. If all restaurant sales were classed as travel and tourism, for example, the statistic would be artificially inflated by sales to residents. However, excluding all restaurant revenues would be as deceptive.

According to Clawson and Knetsch (1966) and Mitchell (1984), efforts to define tourism are complicated by our socioeconomic system’s deep interconnectedness. In terms of philosophical approach, methodological orientation, or investigational goal, tourism studies are frequently set at odds. A wide range of tourist definitions, each with its own set of disciplinary characteristics, influence research projects in diverse fields. Tourism, for example, has a lot in common with recreation and leisure studies in terms of essential traits and theoretical foundations. The terms ‘leisure, “recreation,’ and ‘tourism,’ according to Jansen-Verbeke and Dietvorst (1987), constitute a loose, harmonic unity that emphasizes on the experience and activity-based elements that typify these concepts. Economic and technical/statistical definitions, on the other hand, tend to overlook the human experiencing aspects of the term in favor of a method focused on the movement of people across political borders and the amount of money generated as a result of that movement (Fennell, 2015).

The interaction between tourism and other disciplines, such as psychology, sociology, anthropology, geography, and economics, appears to have defined the face of tourism (Fennell, 2015). Despite its heavy dependence on such disciplines, others, such as Leiper (1981), have pushed for a shift away from them in favor of a separate tourism discipline. According to Leiper, the way we should approach the tourism industry should be based on its structure, which he sees as an open system of five elements interacting with larger environments: (1) a dynamic human element; (2) a generating region; (3) a transit region; (4) a destination region; and (5) the tourist industry.

This definition is similar to that of Mathieson and Wall (1982), who see tourism as consisting of three basic elements: (1) a dynamic element, which involves travel to a specific destination; (2) a static element, which involves a stay at the destination; and (3) a consequential element, which is concerned with the economic, social, and physical consequences of the above two. Others, such as Mill and Morrison, define tourism as a collection of interconnected components. The system works like a spider’s web: if you touch one area of it, reverberations can be felt all over (Mill and Morrison 1985: xix). Market (reaching the marketplace), Travel (the purchasing of travel items), Destination (the shape of travel demand), and Marketing are all aspects of their tourism system (the selling of travel) (Fennell, 2015). Because defining tourism is difficult, Smith (1990a) believes it is more practical to accept the existence of multiple definitions, each meant to serve a distinct goal. This may turn out to be the most practical course of action to take (Fennell, 2015).