The visible horizon, including trees, buildings, mountains and the like, dividing the sky into an upper portion, which is visible, and a lower portion, which is not. Generally at least somewhat similar to, but not identical to, the astronomical horizon.
A skyline is best described as the overall or partial view or relief of a city's tall buildings and structures consisting of many skyscrapers. It can also be described as the artificial horizon that a city's overall structure creates. Skylines serve as a kind of fingerprint of a city, as no two skylines are alike.