What is horizontal farming?

Although any form of agriculture that is not carried out vertically (vertical farming) is called horizontal, the term has prevailed to be used in hydroponics.

Hydroponics is the cultivation of plants without soil, with the roots growing either in inert materials and absorbing the nutrients from passing nutrient solution or growing directed to it and inert material being used only for their fixation. Unlike vertical farming, where there are many plant levels per unit of land area, horizontal is done on a single layer.