Although an absolute definition of complexity remains elusive, the term is generally used to characterize a phenomenon that emerges from a collection of objects that interact with each other in various ways – a system. A key aspect of complexity is that the emergent behavior arises as a result of the collective nature of the whole system and without direction from a central authority.
A classic example is a flock of birds. The collection of birds move as one body, but no single bird is directing the flight behavior. Furthermore, people, cells, robots, and numerous other ‘things’ can work collectively to create amazing emergent behaviors. Economies, social networks, cancer, contagion spreading – all are complex systems that impact our financial stability, daily interactions, and general health. Complexity underlies some of society's most pressing issues, and an approach that embraces the non-equilibrium and highly connected nature of a system can lead to solutions that would be otherwise inaccessible.