The viewing frustum for a Camera defines the volume of 3D space that is rendered. This is defined in terms of a front clipping distance, a far clipping distance and the rectangle at the front clipping distance. P01
Computer-generated objects can be projected into an artificial viewing area, called a frustum. A frustum is in the form of a truncated pyramid, shown in Figure 5-3, between the base of the viewing volume, called the far plane, and the near plane.
In 3D programming: A pyramid-like shape with its point at the 'camera', pointing in the direction that you are viewing, and the base representing the far clip plane. This geometric shape contains all objects that are visible.
In GL, a truncated, four-sided pyramid; that is, a pyramid with the point cut off. In a perspective projection, the shape of the clipping volume is a frustum. The bottom of the frustum is referred to the far clipping plane, the top of the frustum is the near clipping plane, and the sides are respectively the top, left, bottom, and right clipping planes. In an orthographic projection, the clipping volume is a parallelepiped.
A frustum is the portion of a solid – normally a cone or pyramid – which lies between two parallel planes cutting the solid. Degenerate cases are obtained for finite solids by cutting with a single plane only.