The pentagram is a five-pointed star, encircled.

With the star pointing up, it is said to be a symbol of the spirit. This is shown in the stereotypical da Vinci picture, with the man, his limbs each drawn in a few positions.

This allegedly represents the five (or six) spiritual points of the body: the head, the arms, the legs, and the centre.

The Satchakra-Narupana by Purnananda gives the spiritual centres in different positions, mostly in the torso. For this reason, I believe the first five positions in the da Vinci pentagram signal the parts used for accepting energy, and the Satchakra-Narupana signal the chakra for changing the energy into different forms.

When the star points downward, the pentagram is said to be representative of the flesh, or Baphomet, the scapegoat. Baphomet, being a goat that was once sacrificed for someone's sins in the Bible, is somehow related to Satan.

Although I can't see the connection, I assume it has something to do with the fact that they both are blamed.

Sometimes, mostly in Satanist circles, the Baphomet is shown with a picture of a goat's head inside. This image appears on the front of The Satanic Bible, by Anton Szandor LaVey.