What term is used to describe someone that is not affected by passion or feeling?

The term that describes someone who is not affected by passion or feeling is "stoic." This word is derived from Stoicism, an ancient philosophical school that teaches the development of self-control and fortitude as a means to overcome destructive emotions. A stoic individual displays emotional resilience, remaining unaffected by external circumstances, thereby maintaining a calm and rational demeanor even in challenging situations.

In contrast, the other terms provided do not convey the same meaning. "Mundane" refers to something that is ordinary or lacking excitement, while "parochial" describes a narrow or limited perspective, often pertaining to local concerns. "Mediocre" denotes something that is of average quality or not exceptional but doesn’t specifically relate to emotional detachment. Thus, "stoic" is the most accurate term to describe someone who remains unaffected by emotion.