What is that thing on the top of a beret?

The thing on the top of a beret is called a "tassel" or "cord." It is typically made of the same material as the beret and can serve both decorative and symbolic purposes. In some military or ceremonial contexts, the positioning and color of the tassel may signify rank or unit affiliation. The tassel adds to the distinctive look of the beret, contributing to its unique style.