So what do we mean exactly when we say synchronicity? In Jungian psychology, synchronicity is defined as meaningful and causally related connections between physical and mental events.

So, in other words, physical events occur that have some inner meaning. But what’s the point of them? Jung believed there is a deeper level of the collective unconscious that underpinned the physical world.

As such, in his mind, synchronicities break through this collective unconscious to prod our conscious minds. Jung suggested the reason synchronicities occur is so the universe can tell or teach us something important.
This is a good little history lesson on the origin of the thought and term synchronicity.

Jungian Psychology and Its Little-Known Connection with Synchronicity — by Janey D.