Tactical voting happens when a person votes for someone other than their favorite candidate in a way to either help their favorite or achieve some other goal. This may happen in national or local elections, or even in elections for clubs and homeowner associations.
Say 5 people are running as candidates for board members, but only 3 will be elected. For the following situations except the last, let's say you get 1 vote.
Another common situation happens in primary elections, where members of one party may temporarily 'cross over' to the other party to support a candidate who is getting fewer votes, hoping their favorite will face weak competition in the main election. This type of negative voting is popular but often considered unethical.
Many experts question tactical voting in that it can undermine a democratic outcome. That is, ethical voters may believe it more important how a candidate wins than who wins. Others feel the end justifies the means. Most researchers tend to frown on tactical voting.