The term "root flare" refers to the surface roots that provide visual balance to a tree. Ideally, the surface roots are visible on all sides of the trunk. The root flare is also called "Nebari" in Japanese. There are different techniques to create or improve the root flare of a bonsai, such as regular root pruning or air layering methods. The root flare is crucial for the design of bonsai, as it creates a sense of stability and strength.