“…The triquetra is three interlocking pieces that represent the place where three circles would overlap. In Christian Ireland and other areas, the triquetra was used to represent the Holy Trinity, but the symbol itself far predates Christianity. It has been speculated that the triquetra was a Celtic symbol of feminine spirituality, but it has also been found as a symbol of Odin in the Nordic lands. Some Pagan writers claim that the triquetra is the symbol of a triple goddess, but there is no scholarly evidence of a connection between any triune goddess and this particular symbol. In some modern traditions, it represents the connection of mind, body and soul, and in Celtic-based Pagan groups it is symbolic of the three realms of earth, sea and sky.
Although commonly referred to as Celtic, the triquetra also appears on a number of Nordic inscriptions. It has been discovered on 11th-century runestones in Sweden, as well as on Germanic coins. There is a strong similarity between the triquetra and the Norse valknut design, which is a symbol of Odin himself. In Celtic artwork, the triquetra has been found in the Book of Kells and other illumintated manuscripts, and it often appears in metalworking and jewelry. Interestingly, the triquetra rarely appears all by itself, which has led some scholars to speculate that it was originally created for use just as filler material — in other words, if you had a blank space in your artwork, you could squeeze a triquetra in there!
Occasionally, the triquetra appears within a circle, or with a circle overlapping the three pieces.
For modern Pagans and NeoWiccans, the triquetra is just as often associated with the television show Charmed, in which it represents the “power of three” — the combined magical abilities of three sisters who are the show’s main characters.”-Patti Wigington