Concept means

Concept

In contextual reading, a term is interpreted by the explicit definition and contrasts supplied by the passage, not by every broad dictionary association.

A concept is an abstract mental representation formed by generalizing earlier perceptions; a percept is direct observation through the senses.

Application

The passage directly states that direct observation through the senses is a percept, whereas the mental image is a concept. Therefore, the definition asked for is “a mental image.”

Contrast

• A mental image: this is the passage’s stated meaning of a concept.

• A reality: the passage associates reality with percepts, not with the theoretical mental image.

• An idea put into language form: language supplies symbols for mental images, but the passage does not define the concept as the linguistic expression itself.

• A mental image, a reality, and an idea put into language—jointly: this combines three distinct descriptions into one definition.

Cross-check and result

The passage’s contrast between percept and concept independently confirms the distinction: percept corresponds to sensed reality, while concept corresponds to the mental image. Hence the answer is “a mental image.”