Horizon

Noun

1. The visible horizontal line (in all directions) where the sky appears to meet the earth in the distance.

   "A tall building was visible on the whole sweep of the horizon."

2. The range or limit of one's knowledge, experience or interest; a boundary or threshold.

   "Some students take a gap year after finishing high school to broaden their horizons."

3. The range or limit of any dimension in which one exists.
4. A specific layer of soil, or stratum
5. A cultural sub-period or level within a more encompassing time period.