  The concept of "self-organized criticality" (SOC) has been introduced by Bak,
Tang, and Wiesenfeld (1987) to describe the statistics of avalanches on the
surface of a sandpile with a critical slope, which produces a scale-free
powerlaw size distribution of avalanches. In the meantime, SOC behavior has
been identified in many nonlinear dissipative systems that are driven to a
critical state. On a most general level, SOC is the statistics of coherent
nonlinear processes, in contrast to the Poisson statistics of incoherent random
processes. The SOC concept has been applied to laboratory experiments (of rice
or sand piles), to human activities (population growth, language, economy,
traffic jams, wars), to biophysics, geophysics (earthquakes, landslides, forest
fires), magnetospheric physics, solar physics (flares), stellar physics
(flares, cataclysmic variables, accretion disks, black holes, pulsar glitches,
gamma ray bursts), and to galactic physics and cosmology.
