Like a Christian cross, the pentagram tends to be the religious symbol of the Pagan path. It encompasses our Elemental beliefs and is one of the strongest protective amulets there is.
The Pentagram dates back thousands of years to pre-Babylonian Sumer, roughly 3500 B.C. Many religions have used this symbol. It goes by many names, including the Druid’s Foot and the Witch’s Star.
Each point of the Pentagram represents one of the five Metaphysical Elements of the Ancients. The top point represents Spirit. The upper left point represents Air. The upper right point represents Water. The lower left point represents Earth. The lower right point represents Fire. In this way, the Pentagram represents Spirit ruling over the four physical Elements.
The Pentacle is just the Pentagram with a circle around it, which symbolizes eternity, totality and unity. It emphasizes the inter-connectivity of all of the Elements; the direct and indirect relation of one Element to the other.
In Modern Paganism it’s also a unifying symbol of our community as well as the physical symbol of the Element of Earth when placed on the altar.
Source: Pentagram VS. Pentacle