Synchronization :
firefly

Systems operating with all their parts in synchrony are said to be synchronous.
Synchronization is a phenomena where  many random units operate a  in unison 
when they are coupled. Take an example of "flashing fire flies" on a tree .  You
would see  flashes  ( one or two flies flash and then suddenly almost all of them
flash and then it repeats). How do they know when to flash ?
 
Synchronization is a collective behaviour seen in nature. Cardiac pacemakers
singing crickets and firing neurons, all function in unison.

Several coupled units  can go through a phase transition from a  random or
de-synchronized phase to a synchronized phase.  Generically, these
transitions belongs to the universality class of DP or KPZ. The Langevin
theory predicts that, even a first order synchronization transition is  possible.

In one of my work (the first one, below) I  tried to construct a  model system
 to see the observed discontinuous transition.


Ref :
Title: First-order Synchronization Transition in Locally
Coupled Maps, P. K. Mohanty,  Phys. Rev.  E 70, 045202(R), 

  arXiv:cond-mat/0507037 [ps, pdf, other][ J. Phys. A 39, L415 (2006)]
Title: A new approach to partial synchronization in globally coupled rotators