Synchronicity was a term originally created by Carl Jung to describe the meaningful coincidences that occur in one's life.  The term has been popularized in the mass media by the Police's album Synchronicity, and more recently by The Celestine Prophecy by James Redfield.

Synchronicity can best be described by examples.   A friend of mine was wondering whether or not he should follow through on his decision to get a divorce.  He turned on the radio and found an ad for available apartments.  He smiled and knew what he needed to do.

Another example would be thinking of a friend and receiving a phone call from that friend at that time.  Another example would be watching a movie and seeing within the story of that film a metaphor for your own life situation.  When you are open to synchronistic events, they can help you make choices in your life, because they are a form of guidance from the Universe.

Not many people are comfortable at first with the idea that the Universe is giving them guidance.  What helps to make it more understandable is to see all energy and matter as interconnected.  One part of the web affects the other.  Therefore, all parts of the web are informing each other at all times.  We are undeniably interconnected.  Therefore, it would make sense that two seemingly disconnected events (thinking about leaving one's partner and turning on the radio) are actually interconnected.

Tarot cards, and other forms of divination such as runes and I Ching coins are examples of tools that can be used to divine patterns and aids in understanding guiding energies.  The people you meet or simply run into on the street; the shirt that someone you walk by is wearing; the license plate or bumper sticker of the car in front of you.  These are all examples of synchronicity.  No, you're not crazy.  You are part of the Universe, and the Universe is communicating with itself.