Pentagram

A pentagram is a five-pointed star, which has many symbolic meanings in magic. It was originally a symbol of good energy, before the forces of evil stole it giving it negative connotations in the public eye.

A spiritual nexus is the point in the center of a geographical pentagram created by the five spiritual elements (Earth, Fire, Water, Wood, Metal). The Halliwell Manor was located at the center of a spiritual nexus, making it a battleground for good and evil. The Charmed Ones realized this in 1999 when the Woogyman tried to take over the manor.

History
While battling the Four Horsemen of the Apocalypse, the Charmed Ones inadvertently formed a Pentagram with three of their members with Prudence and War in the center. This combined with each of their magics trying to destroy the others formed a vortex that trapped Prue and the Horseman of War in another plane. Both of them were rescued from that plane when they formed the pentagram again.

The sorcerer Mordaunt used a table inscribed with a pentagram to cast a spell to absorb the powers of several demons, allowing him to claim Excalibur.

When demons seek to claim a territory, they can kill innocents on the five points of a pentagram. Successfully killing five innocents would secure their territory and prevent other demons from reclaiming it. A demon named Malvoc and his clan attempted this in late 2004, though they were ultimately vanquished.

Notes and Trivia

 * A reversed pentagram is on the cover of the Grimoire.
 * The Triad wore reversed pentagrams on their robes.