The "Charmed" symbol, known as a triquetra, carries several different meanings in a variety of cultural groups, each of which boils down to a unification of three distinct forces. In Christianity, this is the Holy Trinity, while in Celtic, Norse and Druidic cultures, it may have been any of several different unified forces.
While the Christian Trinity is the most common symbolism behind the triquetra, other meanings are equally valid. As the symbol itself predates Christ by several hundred years, it is difficult to divest it of that early meaning. Depending on where it is depicted, these meanings may include the three primary elements (earth, air and water), the cycle of life (birth, death and rebirth) or the three promises of marriage (love, honor and protect). This last example is often reinforced due to the use of the triquetra in wedding regalia, from traditional claddaugh rings to the vestments of the bride during a Celtic ceremony. The same symbol has also become synonymous with non-Christian characters in both movies and television and has been linked closely to the resurgence of neo-paganism in the world. In short, the symbol's meaning is entirely dependant on the context in which it is used.