A pentagram was an ancient symbol of the occult. It was usually represented by a five-pointed star encircled by a continuous ring. This could be displayed one point upwards, or two points upwards, depending on its use.
Spock drew a pentagram, which he referred to a "mystic symbol", as he attempted to toy with the art of magic. While standing inside the pentagram, he successfully moved a Vulcan chess piece with his newfound "powers."