Complex sentence: In non-equilibrium systems there are net flows of matter or energy, or phase changes are occurring; if such changes can be triggered to occur in a system in which they are not already occurring, it is said to be in a metastable equilibrium.
Split into simpler sentences: In non-equilibrium systems, by contrast, there are net flows of matter or energy, or phase changes. If such changes can be triggered to occur in a system in which they are not already occurring, it is said to be in a metastable equilibrium.