Strategic or tactical voting is a situation where a voter considers the possible ballots cast by other voters in order to maximize their satisfaction with the election's results. For example, in plurality or instant-runoff, a voter may recognize their favorite candidate is unlikely to win and so instead support a candidate they think is more likely to win.
Stenciling on a Parisian sidewalk ahead of the first round of the 2017 French presidential election invoking "votez utile" (strategic voting) as a reason for voters to vote for François Fillon instead of Emmanuel Macron