The term "PointerDown" refers to an event in user interface programming that occurs when a pointing device, such as a mouse or touchscreen, makes contact with a surface. This event is crucial for detecting user interactions, allowing applications to respond when a user presses down on a button or screen. In many programming environments, such as JavaScript or Unity, the "PointerDown" event can trigger specific actions, like starting a drag operation or initiating a selection. It is part of a broader set of pointer events that also includes "PointerUp" and "PointerMove," which help developers create interactive and responsive applications.