Which term represents an act of elegance and refinement in behavior?

The term that represents an act of elegance and refinement in behavior is "decorum." This word is often used to describe behavior that is proper, dignified, and in good taste, especially in social situations. It implies an adherence to established standards of conduct, and those who exhibit decorum are seen as exhibiting grace and respectfulness, which aligns with the concept of elegance.

In contrast, "dainty" generally refers to something small, delicate, or particularly graceful, but does not specifically encompass the broader ethical behavior or social norms indicated by decorum. "Deluge" refers to a severe flood or an overwhelming amount of something, and "decimate" means to destroy a significant portion of something. Neither of these terms relates to behavior or elegance, making decorum the most fitting choice for the concept being described.