Noun
The part of a solid next the base, formed by cutting off the, top; or the part of any solid, as of a cone, pyramid, etc., between two planes, which may be either parallel or inclined to each other.
One of the drums of the shaft of a column.
Source: Webster's dictionaryWhen a camera is selected in the view, its frustum is visible in the view. Source: Internet
You can also verify the clip planes by taking a look at the Camera's frustum wireframe in the Scene view. Source: Internet