Which term refers to an essential component?

The term that refers to an essential component is "cardinal." In this context, "cardinal" signifies something that is fundamental or of primary importance. It is often used to describe aspects that are critical to the existence or function of something. For instance, in mathematics, cardinal numbers indicate quantity and form the basis of counting, indicating their essential nature in understanding number systems.

The other options imply lesser importance. "Secondary" suggests a level of importance that is lower than primary, while "marginal" denotes something that exists at the edge or periphery, implying it is not central. "Insignificant" conveys a lack of importance altogether. Thus, "cardinal" is the only term that directly aligns with the idea of being an essential component.