It is one of the ashtamangala (auspicious symbol). It can look somewhat like a fleur-de-lis, an endless knot, a flower or diamond-shaped symbol.
The endless knot is a closed, graphic ornament composed of right-angled, intertwined lines. In its earliest form, it appears as a “naga symbol” with two stylized snakes. Ultimately, it evolved into the endless knot, which has also been described as the “love knot.” For Tibetans, the intertwining of the lines depicts how all phenomena are intertwined and dependent on causes and conditions. The knot is comprised of a pattern with no gaps or breaks, which at once expresses motion and rest in a representational form of great simplicity and fully balanced harmony. . It is conceived as being auspicious in the highest degree, and its “mode of operation” is always experienced at many levels. Since all phenomena are interrelated, the placing of the endless knot on a gift or on a greeting card is understood to establish an auspicious connection between the giver and the recipient. At the same time, the recipient is supposed to be linked up with favorable circumstances in the future, reminded that future positive effects have their roots in the causes of the present, which is what karma is all about.
Since the knot has no beginning and no end, it also symbolizes the infinite knowledge of the Buddha.