What is the legal test for a waiver or forfeiture of a right?

Errors not objected to at trial are generally subject to waiver or forfeiture. "Forfeiture is the failure to make a timely assertion of a right, whereas waiver is the intentional relinquishment or abandonment of a known right." United States v. Perez , 116 F.3d 840, 845 (9th Cir. 1997) (en banc) (internal quotation marks omitted); see also Crowley v. EpiCept Corp. , 883 F.3d 739, 748 (9th Cir. 2018) (per curiam) (applying same standard in civil context). "Forfeited rights are reviewable for plain error, while waived rights are not." Id .

Under plain error review, we may reverse only where: (1) there was an error; (2) the error was obvious; (3) the error affected substantial rights; and, (4) the error seriously affects the fairness, integrity, or public reputation of judicial proceedings. See C.B. v. City of Sonora , 769 F.3d 1005, 101819 (9th Cir. 2014) (en banc). In other words, plain error requires reversal where "review is necessary to prevent a miscarriage of justice." Draper v. Rosario , 836 F.3d 1072, 1085 (9th Cir. 2016) (internal quotation marks omitted).