From Wikipedia:

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 the Jews. The pentagram has magical associations. Many people who practice Neopagan faiths wear jewelry incorporating the symbol. Christiansonce commonly used the pentagram to represent the five wounds of Jesus. The pentagram has associations with Freemasonry and is also used as a symbol by other belief systems.A pentagram (sometimes known as a pentalpha, pentangle or star pentagon) is the shape of a five-pointed star.

The word pentagram comes from the Greek word πεντάγραμμον (pentagrammon), from πέντε (pente), "five" + γραμμή (grammē), "line". The word "pentacle" is sometimes used synonymously with "pentagram". The word pentalpha is a learned modern (17th-century) revival of a post-classical Greek name of the shape.