The circle which bounds that part of the earth's surface visible to a spectator from a given point; the apparent junction of the earth and sky.
- The apparent intersection of the earth and sky as seen by an observer. Also called apparent horizon.
- Astronomy The sensible horizon.
- Astronomy The celestial horizon.
- Astronomy The limit of the theoretically possible universe.
- The range of one's knowledge, experience, or interest.
- Geology A specific position in a stratigraphic column, such as the location of one or more fossils, that serves to identify the stratum with a particular period.
- Geology A specific layer of soil or subsoil in a vertical cross section of land.
- Archaeology A period during which the influence of a specified culture spread rapidly over a defined area: artifacts associated with the Olmec horizon in Mesoamerica.