Triquetra

The Triquetra meaning "three-cornered" in Latin, has three distinct, yet interlocked points.
The symbol technically represents the 3 aspects of the feminine life cycle, the maiden, the mother and the crone but more frequently represents the 3 fold nature.
This symbol were adopted by Christians as the sign for the Holy Trinity (God the Father, God the Son and God The Holy Spirit). Also, it could represent three fishes ("Pisces").
In Christian Ireland and other areas, the triquetra was used to represent the Holy Trinity, but the symbol itself far predates Christianity.
It has also been found as a symbol of Odin in the Nordic lands.
Occasionally, the triquetra appears within a circle, or with a circle overlapping the three pieces.