Voting in an election would be considered both a Civic Duty and a Civic Responsibility. However, if you have to choose one, the more commonly used term is A Civic Duty. Civic duties are obligations that citizens are expected to perform, such as voting, paying taxes, and serving on juries. Civic responsibilities, on the other hand, refer to actions that are encouraged but not legally required.
So, the answer is:
A Civic Duty.