The terms pentagram and pentacle have slightly different star designs, but the designs themselves are often used by the general public synonymously or interchangeably.
A pentagram is a five-pointed star. The word pentagram is Greek and comes from the word pente which means five, "5", and graphein, which means "to write." The pentagram has been in use unofficially since ancient times vaguely indicating spirituality.
A pentacle is a five-pointed star within a circle.
Today, a pentacle pointed in the upward position is popularly used as a symbol to represent modern revivalist paganism as well as loosely representing the Traditional Craft.
Note: A pentacle pointed in the downward position is used very differently. It is used exclusively as a symbol to represent Satanism. Satanism is a Roman Catholic heresy that is primarily an American phenomenon and should not be confused with any form of Traditional Craft.