The following comes from Wikipedia.
A pentagram (sometimes known as a pentalpha or pentangle or, more formally, as a star pentagon) is the shape of a five-pointed star drawn with five straight strokes. The word pentagram comes from the Greek word πεντάγραμμον (pentagrammon), a noun form of πεντάγραμμος (pentagrammos) or πεντέγραμμος (pentegrammos), a word meaning roughly "five-lined" or "five lines".
Pentagrams were used symbolically in ancient Greece and Babylonia, and are used today as a symbol of faith by many Wiccans, akin to the use of the cross by Christians and the Star of David by Jews. The pentagram has magical associations, and many people who practice Neopagan faiths wear jewelry incorporating the symbol. Christians once more commonly used the pentagram to represent the five wounds of Jesus, and it also has associations within Freemasonry.
The word "pentacle" is sometimes used synonymously with "pentagram", and this usage is borne out by the Oxford English Dictionary, although that work specifies that a circumscription makes the shape more particularly a pentacle. Wiccans and Neo-pagans often make use of this more specific definition for a pentagram enclosed in a circle.
I wear mine almost every day and it feels like a talisman, as if I won't be safe without it. Interesting, isn't it how we use these tools to aid our passage through life.