The belt encircles its wearer. The circle is a universal symbol of wholeness and harmony, and symbolizes the totality of the universe. The circularity of the belt reinforces the circular cycle of Taekwondo training; the fact that, after years of training, one realizes that the true essence of Taekwondo existed at the beginning.
As a practical matter, the Taekwondo belt holds the uniform closed, but its real significance is far greater than merely being a clasp or even a signifier of rank. The belt has symbolic meanings, both in eastern philosophy and in its color.