What term describes the slight convexity applied to columns to correct optical illusions?

The term that describes the slight convexity applied to columns to correct optical illusions is entasis. This architectural technique involves a subtle curvature in columns, especially in classical architecture. The primary purpose of entasis is to counteract the visual perception of the column appearing to be concave or straight when it is actually not. Human visual perception can create illusions, making perfectly straight lines seem to bow or curving at their centers. By incorporating a slight bulge into the design, architects ensure that the columns maintain an aesthetically pleasing and visually correct appearance.

It is essential to understand that terms like "enthasis" do not represent a recognized concept within architecture. Similarly, the options including "none of the above" or "all of the above" would not apply in this context since entasis is indeed the established terminology directly related to the described architectural feature. This understanding of entasis is critical for appreciating how subtle adjustments in architectural design can enhance the overall visual integrity of structures.