Final answer:
Specialist travel intermediaries like incentive travel houses, destination management companies, and professional conference organizers belong to the tourism sector of the travel trade system, which is part of the tertiary service industry.
Step-by-step explanation:
Incentive travel houses, destination management companies and professional conference organizers are all specialist travel intermediaries that primarily operate within the tourism sector of the travel trade system. These entities specialize in creating, organizing, and managing travel experiences catered to rewarding employees (incentive travel), handling the logistics for travelers in a particular destination (destination management), and organizing professional gatherings (conferences and events).
While these services may overlap with event management, particularly in the case of professional conference organizers, their core functions align them with the broader scope of tourism, which encompasses aspects of accommodation, transportation, and events. The tertiary sector of the economy, which includes service industries such as tourism, is responsible for handling goods and services and has grown substantially, dominating employment in regions like the US. The tourism industry is a significant source of income, especially for areas that rely on natural beauty and relaxation to attract visitors.