Definition of "horizon"

horizon

/həˈɹaɪ.zən/

noun
plural horizons
1. The visible horizontal line (in all directions) where the sky appears to meet the earth in the distance.
2. (figuratively) The range or limit of one's knowledge, experience or interest; a boundary or threshold.
  Quotations
  The Indians of the Americas totaled no less than 70 million when the foreign conquerors appeared on the horizon; a century and a half later they had been reduced to 3.5 million.
  1997, Eduardo Galeano, Open Veins of Latin America: Five Centuries of the Pillage of a Continent, Monthly Review Press, page 38
3. The range or limit of any dimension in which one exists.
  Quotations
  Only mortality, this irreducible and primordial horizon, that very horizon which, in Being and Time, Heidegger so compellingly revealed as the unsurpassable and defining possibility, remains.
  2003, Miguel de Beistegui, Thinking with Heidegger: Displacements, page 157
4. (geology) A specific layer of soil, or stratum
5. (archaeology, chiefly US) A cultural sub-period or level within a more encompassing time period.
6. Any level line or surface.
7. (chess) The point at which a computer chess algorithm stops searching for further moves.