  For some forms of steady heating, coronal loops are in a state of thermal
nonequilibrium and evolve in a manner that includes accelerated cooling, often
resulting in the formation of a cold condensation. This is frequently confused
with thermal instability, but the two are in fact fundamentally different. We
explain the distinction and discuss situations where they may be
interconnected. Large-amplitude perturbations, perhaps associated with MHD
waves, likely play a role in explaining phenomena that have been attributed to
thermal nonequilibrium but also seem to require cross-field communication.
