Pythagoras used it as a symbol of health and his followers wore them in order to recognize one another.
they called it the "Pentalpha," because it consisted of five interwoven alphas: the Greek letter A,
which stood for birth and beginnings.

In Medieval times, some Christian knights used the pentagram as their symbol.

 In Greece it was the symbol of  Demeter's daughter Kore, the Goddess of vegetation and the fruits of the field, because the apple contains a star composed of five seeds in its core.
Today gypsies call the five-seeded pentacle in the apple "the Star of Knowledge."

 In Egypt a five-pointed star represented the great underground womb of  Mother Earth.

The Celtic tribes also saw it is a sign of the Goddess of the Underworld, Morgan.

In Babylon the pentacle was an amulet of protection and healing.

In Judeo-Christian traditions the pentacle was the first of the Seven Seals,
which represented the secret name of God.

King Solomon wore a pentacle on his ring as a sign of  his power to work magic.

Among the old European tribespeople the pentacle represented the Horned God, a shape shifter who had five manifestations: a human, a bull, a ram, a goat, and a stag.

The Celtic hero Gawain had a pentacle enscribed on his shield.

 To the Jews, it symbolically designated the Pentateauch, The Five Books of Moses.

Early Christians recognized it as pointing out the five Stigmata -- the  wounds Christ suffered on the Cross.

It has survived under a variety of titles, including "The Druid's Foot" and "The Witch's Star."

The pentagram in a circle may also represent a human with their legs and arms outstretched,surrounded by universal wisdom or the "Goddess" - humankind at one with the environment.

The five points also represent the five senses, through which earthly knowledge enters the mind. The center can stand for the sixth sense, the deep unconscious, or the ethereal connection of each human being with the All or the Higher Self.

Can also be seen as representing the unending and unbroken cycle of the five stages of life-birth, initiation, adulthood, repose, and death.

Also signifies the rulership of  Higher Mind over the lower elements of Human Nature. In this context it represents the awakening of Cosmic Consciousness and  reaching beyond the realms of physical form and perception limited to the five physical senses. It allows the infinite possibilities that exist within the Universe and frees us to explore and to grow. The pentacle tells us that we have the ability to bring Spirit to Earth

The number five is attributed to the influence of Mars. Thus some Wiccans think of the five pointed star within the circle as force or power contained and controlled by divine wisdom

Used inverted, with the top point pointed downward, it represents a second or third degree status in some traditional  groups. Many of these groups have since substituted a triangle form for the same degrees because of the association of the  inverted form of the pentacle with Satanism and black magic.

It is the simplest form of star shape that can be drawn unicursally - with a single line.
- hence it is sometimes called the Endless Knot.

Many Wiccans wear a pentacle pendant or ring as a sign of their religion or as an amulet or talisman.

The pentacle crafted from silver represents Moon energy and psychic forces.

The same symbol made in gold represents the Sun energies of  power and strength.

Many pentacles come with embedded stones which can represent birth months or a particular energy  that the wearer wants to attract.