<p><strong>Noun</strong></p><ul><li>the line or circle that forms the apparent boundary between earth and sky</li><li>the small circle of the celestial sphere whose plane is tangent to the earth at the position of a given observer</li><li>the great circle of the celestial sphere whose plane passes through the center of the earth and is parallel to the sensible horizon</li><li>the limit or range of perception, knowledge, or the like</li><li>the scope of a person's interest, education, understanding, etc.</li><li>a thin, distinctive stratum useful for stratigraphic correlation</li><li>any of the series of distinctive layers found in a vertical cross-section of any well-developed soil</li></ul>