  Bounding volume results in discreteness of eigenmodes in wave systems. This
leads to a depletion or complete loss of wave resonances (three-wave,
four-wave, etc.), which has a strong effect on Wave Turbulence, (WT) i.e. on
the statistical behavior of broadband sets of weakly nonlinear waves. This
paper describes three different regimes of WT realizable for different levels
of the wave excitations: Discrete, mesoscopic and kinetic WT. Discrete WT
comprises chaotic dynamics of interacting wave "clusters" consisting of
discrete (often finite) number of connected resonant wave triads (or quarters).
Kinetic WT refers to the infinite-box theory, described by well-known
wave-kinetic equations. Mesoscopic WT is a regime in which either the discrete
and the kinetic evolutions alternate, or when none of these two types is purely
realized. We argue that in mesoscopic systems the wave spectrum experiences a
sandpile behavior. Importantly, the mesoscopic regime is realized for a broad
range of wave amplitudes which typically spans over several orders on
magnitude, and not just for a particular intermediate level.
