An election in which voters are asked to name their second choice on the ballot is an example of

Instant runoff.

Explanation:

Instant runoff voting(IRV) is defined as the voting method in which a person has the ability to vote according to the preference among two or mores candidates. This voting method is considered in the situation where more than half votes are required to be earned by a candidate in first round of election to win elections.

If the candidate is not able to gain such amount of vote then second round is regulated till the more than half vote are gained. According to the question preferring second option of candidate for ballot is type of instant runoff voting.