Which concept defines a mental category for grouping similar features?

The correct answer focuses on the concept of a "Formal Concept." This term refers to a mental category that is created based on specific, defined criteria and rules. Formal concepts are often derived from characteristics that can be clearly identified and categorized, such as geometric shapes (triangles, squares) or mathematical concepts. These definitions allow for an organized understanding and categorization of similar features.

In contrast, other options delve into broader or less structured domains. For instance, an abstract concept typically involves more generalized ideas that may not have precise boundaries, like love or justice, which can differ greatly in interpretation. An applied concept is oriented towards practical applications, relating theory to real-world scenarios, while a theoretical concept often revolves around hypotheses or models that explain a phenomenon but may not encapsulate specific groups of features.

Thus, "Formal Concept" is the most accurate term for a mental category formed around well-defined similarities.