Final answer:
Entasis is the term used to describe the slight convexity applied to columns in Greek architecture that corrects the optical illusion of concavity. This subtle architectural feature makes columns appear straight and stable, enhancing the overall aesthetic and structural integrity of buildings like the Parthenon.
Step-by-step explanation:
The slight convexity given to a column to correct the optical illusion of concavity is known as entasis. This architectural adjustment was critical in ancient Greek architecture, where builders and architects such as Iktinos and Kallikrates implemented slight adjustments to structures like the Parthenon to account for the perception of human vision. With this technique, columns were crafted to slightly swell in the middle, ensuring they did not appear to taper, enhancing their stability and robustness in the eyes of the beholder.
Entablature components like the architrave, cornice, and frieze rest upon these carefully crafted columns, adding to the structure's grandeur without compromising the optical balance. The Greeks' meticulous approach to architecture, ensuring even the subtlest deviations, such as entasis, helped their structures achieve a dynamic and lifelike appearance, defying the static and lifeless form that comes from perfectly straight lines.