A level horizon is a term used in photography to describe an image where the horizon line is perfectly level or parallel with the top and bottom edges of the frame. 

A level horizon is important because it creates a sense of balance and stability in the image, and helps to avoid visual distortion or confusion. 

When the horizon line is not level, the image can feel tilted or off-kilter, which can be distracting or disorienting to the viewer. Achieving a level horizon can be done through careful composition and use of a tripod, or through post-processing tools such as rotation or cropping. 

Many cameras also have built-in electronic level indicators or grid lines that can help photographers ensure that their images have a level horizon. It is better to get the horizon level in the camera than cropping some of the image in editing.

A level horizon is a fundamental aspect of landscape photography, as it creates a sense of grounding and stability that enhances the natural beauty of the scene.