Which term refers to unnatural or artificial behavior intended to impress others?

The term that refers to unnatural or artificial behavior intended to impress others is "affectation." This word describes a mannerism or behavior that is adopted for the purpose of making an impression, rather than being a genuine expression of one's character or feelings. Individuals may engage in affectation to convey a sense of sophistication, status, or uniqueness, but it often comes across as insincere or pretentious.

In contrast, the other options do not align with this meaning. "Aghast" describes a state of shock or horror, particularly as a reaction to something unexpected or dreadful. "Aggregate" refers to a collection or total made up of various parts and is often used in contexts involving data or statistics. "Ambience" relates to the character or atmosphere of a place, focusing on the mood rather than behavior. Therefore, affectation distinctly captures the essence of artificial behavior aimed at impressing others.