What is the correct term for a child who does not occupy a seat but sits on an adult's lap?

The term "lap child" is the correct designation for a child who does not occupy their own seat during travel but instead sits on an adult's lap. This classification is commonly used in the context of airline travel, where airlines typically allow infants or young children under a certain age to fly for free or at a reduced rate if they are seated in this manner. While the other terms might seem related, they do not specifically describe the situation of a child sitting on an adult's lap during a flight.

"Infant passenger" generally refers to a young child but does not specify the seating arrangement. "Child passenger" encompasses all children who are passengers, regardless of whether they are in a seat or on a lap. "Underage flyer" could refer to any person who is younger than the threshold age for adult pricing or policies but does not pertain specifically to the seating arrangement. Therefore, "lap child" is the most precise term for this specific situation.