What is the forfeiture rule in appeal law?

"The reason for [the forfeiture] rule is that [i]t is both unfair and inefficient to permit a claim of error on appeal that, if timely brought to the attention of the trial court, could have been easily corrected or avoided. [Citations.] [T]he forfeiture rule ensures that the opposing party is given an opportunity to address the objection, and it prevents a party from engaging in gamesmanship by choosing not to object, awaiting the outcome, and then claiming error. [Citation.]" (People v. French (2008) 43 Cal.4th 36, 46, 73 Cal.Rptr.3d 605, 178 P.3d 1100.) "Had [appellant] timely and specifically objected below, the trial court presumably would have had an opportunity to correct, and could have corrected, any error. [Citation.]" (People v. Ortiz , supra , 208 Cal.App.4th at p. 1372, 145 Cal.Rptr.3d 907, fn. omitted.)