What is thermal acclimation?

Several recent contributions to this Journal have reflected on the current usage and understanding of the term acclimation [Bowler, 2005. Acclimation, heat shock and hardening. J. Therm. Biol. 30, 125–130; Loeschcke and Sφrensen, 2005. Acclimation, heat shock and hardening—a response from evolutionary biology. J Therm. Biol. 30, 255–257; Sinclair and Roberts, 2005. Acclimation, shock and hardening in the cold. J. Therm. Biol. 30, 557–562]. As a contribution to this discourse I propose that a look back into the introduction of this term may provide a useful additional insight.