What does "Walled Garden" mean?

Walled Garden:

A Walled Garden describes an unfair advantage held by a company or group of companies that creates an unlevel playing field. A closed ecosystem or a closed platform where the tech provider has control over the app, the content being displayed on it, or the hardware it is run on. A current example of a Walled Garden is AdX. Users of AdX have an unfair advantage (RTB) when bidding for ads, over those who are not members of AdX. Another example of a "walled garden" is the method Apple has employed to require users of its IPhone products to buy new accessories (different chargers and earphones) when updating its iPhones as they roll out new updates. As well, for many years, Apple would void the warranty of any of its computers that were serviced by any other company than Apple. It's an "our way or the highway" method of dealing with customers.

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