The Pentagram is the most commonly used Wiccan symbol. It has many associations and meanings, and this page only reflects my perception of what the pentagram means. Nothing here is dogma.
The top point represents the All, or what is Beyond the Veil. This means the undifferentiated, pure, raw energy stuff (aether, to the Greeks) that is present in all life. A more tangible way to think of it is like being The Force, from Star Wars. This energy is what we tap into when we use magick. The All represents Deity in its purest form. On this plane, there is no polarity.
The two points below represent the God and the Goddess, or the Astral plane. Deity at this level has polarized into Male and Female, each with its own particular set of energies. They vibrate differently, and therefore affect different types of things in very different ways. Their much more specific energies are what we use to focus the energy used in magick. If the All is the energy itself, the God and Goddess are like two funnels, or filters, which manipulate that energy into a form closer to what we can use and understand.
The lowest two points (though not any less important than the other three) represent Male and Female on this plane, the earthly plane. All material things have either male or female energy in them, and most things have both.
That all five points are connected in a continuous line, and surrounded by a circle is no mistake. The three planes are separated from each other only by our perception. The plane Beyond the Veil and the Astral Plane are not literally above the material plane, all three co-exist. Likewise, the separation of male and female energies is a matter of perception. We percieve male and female on the material plane in the two sexes of animals and plants, and even "handedness" in molecules, atoms, and subatomic particles! However, the energies that exist here are nothing more that subsets of the All, and so there is male present in female, yin in yang, and so on. Wicca is really a religion about balance and interdependence, and the pentagram is a perfect symbol of that. The circle is the symbol of the life cycle, and the five-pointed star a diagram of the interactions of life.