Google has Material Design, Microsoft has Fluent and (unofficially) Metro.
About two decades ago, the User Interface for Mac OS X was called Aqua but I do not see this term used in practice as much anymore (it does not even have a StackOverflow tag like Material Design and Microsoft-Metro have).
Is there a specific name (official or unofficial) for the design language across Apple platforms?
While I'm not entirely sure it's 100% analogous to Material Design, I'd say the term you're looking for is Human Interface Guidelines.