I think the classic definitions are fine: - Monopoly: 50%+ of a market - Oligopoly: Just a few companies control most of the market.

Apple has more than 50% of mobile device market share. That means they're a monopoly.

Apple has 100% control of the app market for their device. This is also a classic form of Monopoly, kind of like a company store, but on a national scale.

Meanwhile, the legal definition has shifted because of activist judging by conservative judges, which created the "consumer harm" standard, which is nebulous, and much easier to turn into a wishy-washy judgment call than the actual, original definition. And conveniently lets corporate crony judges make judgments like "look how much consumer benefit there is from iPhones! we could care less how unfair Apple is to app developers," even though the idea that whatever features are in Apple devices that consumers get such benefits from won't still be available to consumers even if there's some anti-monopoly ruling.

Like many things in modern America, there's been extensive intentional erosion of things that shouldn't be controversial by what the founders would have referred to as "factions," IE special interests.