In Chinese art the endless knot (Chinese: 盤長; pán cháng) is one of the eight auspicious symbols or “eight treasures” which were borrowed from Indian Buddhism (which in turn probably borrowed the symbols from earlier Hindu mysticism). Among the eight, the mystic knot is especially popular, since it “ties together” so many different metaphorical concepts.
Since it has no end, the knot is said to represent that which is divine and eternal: essentially it is an Asian version of the infinity symbol. To people who believe in reincarnation, the knot represents samsara, the eternal cycle of birth, life, death, and rebirth in which all living beings are imprisoned. Each different faith conceives of such endlessness differently and to different worshippers the knot has different sources and varied meanings. In Hindu religious paintings the knot was found upon the breast of Vishnu the preserver of the universe, while Buddhists see it as the intestines of the Buddha. To some it is a symbol of individual longevity, while others regard it as emblematic of the eternal nature of perfect love.
To the most subtle philosophers the knot is itself a sort of koan which cannot be untied or solved. It represents being and non-being knotted together inextricably. The emptiness around the knot defines the knot itself just as emptiness and nothingness pervade and define the apparent reality of existence (according to Buddhist monks and atomic physicists anyway).
My favorite interpretation of the endless knot however is not so abstruse and cosmic but has a rather more human cast. Some sages assert that the knot represents compassion and wisdom, which are components of each other. Without wisdom, compassion is empty and to no avail, whereas without compassion, there is no true wisdom. Each concept grows out of and encompasses the other.