Final answer:
An indicator is a substance that changes color depending on the solution's potential and is used to signal the end point of a redox titration. It does not participate in the reaction but undergoes a color change that indicates the completion of the titration.
Step-by-step explanation:
An indicator plays a special role in redox titrations. It is a substance, typically an organic molecule, that does not participate in the redox reaction but changes color depending on the solution's potential. The color change of the indicator signals the end point of the titration, indicating the completion of the reaction. For example, starch forms a dark blue complex with iodine and changes color from colorless to blue as the reaction progresses.