The phrase "horizontal level" refers to a straight line that is parallel to the ground or a surface. It helps to determine if something is straight or flat. Full definition
Applying your methods of price action with the trend at horizontal levels has helped me recover much of my losses. (learntotradethemarket.com)
In closing, trading horizontal levels with price action signals is the primary technique that I use to analyze and trade the market. (learntotradethemarket.com)
Lift and bend one leg until the thigh is almost at the same horizontal level as your entire upper and your heel is facing the ceiling. (adamkempfitness.com)