What is the "plain error" standard of review on appeal?

^4. The plain error standard of review applies on direct appeal when a defendant fails to raise an objection in the district court. United States v. Ameline, 409 F.3d 1073, 1078 (9th Cir. 2005). "Under the plain error standard, relief is warranted where the district court committed (1) error that (2) is plain; (3) affected substantial rights; and (4) 'seriously affected the fairness, integrity, or public reputation of judicial proceedings.'" United States v. Vargem, 747 F.3d 724, 728 (9th Cir. 2014) (internal quotations omitted).