What does a five-point star within a circle mean?

Answer 1

It is a pentagram which is a popular symbol that is connected to the Freemasons and the Wicca. It is also sometimes a symbol of the devil if two points are up.

Answer 2

The common association for the five-pointed star within a circle (or pentagram) is Wicca, a modern Neo-Pagan religion which is commonly called "witchcraft". Though it has other associations, witches commonly wear it or use it as a symbol of their religion.

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PENTACLE or PENTAGRAM (FIVE-POINTED STAR pointing up): A standard symbol for witches, freemasons, and many other pagan or occult groups. To witches, it represent the four basic elements (wind, water, earth and fire) plus a pantheistic spiritual being such as Gaia or Mother Earth. The pentagram is also "used for protection. to banish energy, or to bring it to you, depending on how it's drawn," wrote a Wiccan visitor. Compare with the next link.
PENTAGRAM (FIVE-POINTED STAR pointing down): Used in occult rituals to direct forces or energies. Often represents satanism, the horned god or various expressions of contemporary occultism, especially when a goat-head is superimposed on the inverted pentagram within a "sacred" circle. See Heartagram, Baphomet and Pentagrams and Pentacles