Per curiam refers to a decision handed down by the court as a whole, without identifying any particular judge as the author. It is the opinion of the court as a single body. Most decisions on the merits by the Supreme Court and other appellate courts in the U.S. are signed by individual justices. Even when such signed opinions are unanimous, they are not termed "per curiam." Per curiam decisions usually deal with issues the court views as relatively non-controversial.
For example, "per curiam affirmed" (PCA) refers to a decison of a court, without identifying any judges by name, finding that the decision of a lower court was correct. Such a decision is often made without rendering an opinion. This may be due to the heavy caseload of a court and need to conserve scarce judicial resources, which prevents a written opinion in every case. A criticism of PCA's is that such a decision and the lack of a record for its basis recludes further review.
