Synchronicity is the experience of two or more events that do not share a direct relationship but have a related means alter or it is also seen as a set of causal unrelated "Coincidence". To count as Synchronicity these events should be unlikely to occur at once. An example would be just finding this page. To future the events, after reading this page you find a copy of the book by Carl Jung laying around somewhere, like the floor of a library or a bus shelter.
Synchronicity in magic, is the belief the universe is guiding you. These random events and (un)pleasant coincidences is the universe leading you somewhere. Synchronicity does not always lead to pleasantries, such as in the case of singer Sting who has still never broken away from his fame in The Police and the songs Synchronicity and Synchronicity II.
In comics, "Synchronicity" is mostly attached to John Constantine. Alan Moore had an obsession with magic and wanted to make John Constantine a working class warlock. John Constantine believes he shows up at the "right place" at the "right time" because he can actually control Synchronicity and it runs like a highway where he can get off as he pleases. John Constantine was originally made in the image of British singer Sting, while he was in the band The Police then wrote two songs dedicated to Synchronicity: "Synchronicity and Synchronicity II".
In the Hellblazer book Roots of Coincidence, writer Andy Diggle explores why John can travel the Highway of Synchronicity. It is not a skill, but a Gift (Curse) from his stillborn twin Brother the Golden Boy.