The Triquetra The triquetra is a triangular Celtic knot design which symbolizes all trinities and especially the realms of Air, Earth and Sea - thus all the world.
Modern Neopagans use the triquetra to symbolize a variety of personal and traditional beliefs. Germanic Neopagan and Heathen groups who use the triquetra to symbolize their faith generally believe it is originally of Norse and Germanic origins. Celtic Reconstructionist Pagans use the triquetra either to represent one of the various triplicities in their cosmology and theology (such as the tripartite division of the world into the realms of Land, Sea and Sky), or as a symbol of one of the specific triple Goddesses, most notably the Morrígan. It is also sometimes used by Wiccans and some New Agers to symbolize either the Wiccan triple goddess or the triplicities of mind, body, and soul.
It was also used by B.E. Druids, it symbolizes Earth, Sea and Sky. Three aspects of Nature that Druids hold sacred
The symbol was later used by Christians as a symbol of the Trinity (Father, Son and Holy Spirit). This appropriation was particularly easy because the triquetra conveniently incorporated three shapes that could be interpreted as Christian symbol.