Generally, slip opinions are judicial decisions that are not published in a reporter. Slip opinions are cited using the docket number. (See Bluebook rule 10.1)
U.S. Supreme Court
Slip opinions are the first version of the Court’s opinions. A slip opinion consists of the majority or principal opinion, any concurring or dissenting opinions written by the Justices, and a prefatory syllabus prepared by the Reporter’s Office that summarizes the decision.
A slip opinion is posted on the SCOTUS website soon after it is issued and remains there for the rest of the Term, when it is published in the U.S. Reports.