United States v. Olano, , is a case that distinguished between forfeiture and waiver

Forfeiture and waiver

Forfeiture and waiver are two concepts that U.S. courts apply in determining whether reversible error has occurred. Waiver is the voluntary relinquishment, surrender or abandonment of some known right or privilege. Forfeiture is the act of losing or surrendering something as a penalty for a mistake...

. Quoting from Johnson v. Zerbst

Johnson v. Zerbst

Johnson v. Zerbst, 304 U.S. 458 , was a United States Supreme Court case, in which the petitioner, Johnson, had been convicted in federal court of feloniously possessing, uttering, and passing counterfeit money in a trial where he had not been represented by an attorney but instead by himself...

, , the Court noted, "Whereas forfeiture is the failure to make the timely assertion of a right, waiver is the "intentional relinquishment or abandonment of a known right.... Whether a particular right is waivable; whether the defendant must participate personally in the waiver; whether certain procedures are required for waiver; and whether the defendant's choice must be particularly informed or voluntary, all depend on the right at stake."

According to the Court, mere forfeiture, as opposed to waiver, does not extinguish an "error" under Rule 52(b) of the Federal Rules of Criminal Procedure

Federal Rules of Criminal Procedure

The Federal Rules of Criminal Procedure are the procedural rules that govern how federal criminal prosecutions are conducted in United States district courts, the general trial courts of the U.S. government. As such, they are the companion to the Federal Rules of Civil Procedure...

. If a legal rule was violated during the District Court proceedings, and if the defendant did not waive the rule, then there has been an "error" within the meaning of Rule 52(b) despite the absence of a timely objection.