Definition of horizons:
(n) :
The visible horizontal line (in all directions) where the sky appears to meet the earth in the distance.
(n) :
(figuratively) The range or limit of one's knowledge, experience or interest; a boundary or threshold.
(n) :
The range or limit of any dimension in which one exists.
(n) :
Any level line or surface.
(n) :
(geology) A specific layer of soil, or stratum
(n) :
(archaeology, chiefly US) A cultural sub-period or level within a more encompassing time period.