Synchronicity is a term first used by Carl Jung. He created it to name the unique phenomena of a coincidence between physical realty and events in the unconscious mind. I experienced one rather humorous example. It occurred in a workshop on Jungian Dream Interpretation. One of the participants was wearing a dress whose commercial logo included the word dreams. She didn't even know it was there until it was noticed by another participant.
I recently experienced a synchronistic event. I had a dream in which a yellow road grader played a central role. It was not in any way a part of day residue. In spite of considerable road construction in our area I hadn't seen such equipment for a long time. The very next day I passed one on the road near our house. It seemed to me a confirmation of the dream's message.
Synchronicity is more than just coincidental juxtaposition of events. It is evidence, for Jung and those who agree with his theories, of the reality of archetypes and the collective unconscious. For Jung, archetypes are realities that exist outside of our concrete world that can effect, direct, and shape our behavior. We can see them in the mythology of ancient Greece, in the character of Tarot Cards, and in the legends and myths of primitive peoples. They have a way of emerging into the dreams of modern people who have no knowledge of any of the sources mentioned. Indeed, Jung began to notice this phenomenon in his early work with patients in a mental hospital.
The collective unconscious in simplistic terms can be thought of as a reservoir of the experiences of all mankind. We gain access to its knowledge and lessons below the level of our deepest personal unconscious. It can erupt into our dreams and make itself known in the phenomenon of Synchronicity.
Wikipedia includes in its article on synchronicity several examples. For movie fans this one is most interesting.
The wardrobe department for The Wizard of Oz unknowingly purchased a coat for character Professor Marvel from a second-hand store, which was later verified to have originally been owned by L. Frank Baum, the author of the novel on which the film was based. (http://en.wikipedia.org/wiki/Synchronicity)
As you can see synchronicity is a fascinating phenomenon. It may be happening to you today and go unnoticed. However, as with dreams, when we begin to pay attention we may notice synchronicity occurring with greater frequency.