"Legal precedent" refers to using judicial decisions made in the past to help determine what is proper for a current case.
When a judge follows a legal precedent, it means that the judge follows a decision made in another case because the facts are similar.
Reliance upon precedent also promotes the expectation that the law is just. The idea that like cases should be treated alike is anchored in the assumption that one person is the legal equal of any other.
Thus, persons in similar situations should not be treated differently except for legally relevant and clearly justifiable reasons.
The application of precedent relies on reasoning by analogy. Analogies can be neither correct nor incorrect but only more or less persuasive. Reasonable persons may come to different yet defensible conclusions about what rule should prevail.
Learn more about the use of precedent at Thefreedictionary.com.