Definitions for "Horizon line"
(n) In a perspective sketch, a horizontal line marking the location where all projection lines from the observer converge.
In linear perspective, the implied or actual line or edge placed on a tw dimensional surface to represent the place in nature where the sky meets the horizontal land or water plane. The horizon line matches the eye level on a two-dimensional surface. Lines or edges parallel to the ground plane and moving away from the viewer appear to converge at vanishing points on the horizon line.
the point atop a drop in which the river visually disappears