In C++ lingo they are called function objects or callables, not functor. You might stumble on code here and there that suffix a class name with Functor but it's not that common.
It's common enough that articles have been written against this usage: https://web.archive.org/web/20170224220253/http://jackieokay...
So this usage of functor may never have been "official", but it's widespread in the community.
† I don't know if the original mistake was his, but he certainly did a lot to spread it.
https://en.cppreference.com/w/cpp/experimental/reflect
https://en.cppreference.com/w/cpp/utility/variant/visit2
https://en.cppreference.com/w/cpp/experimental/parallelism
Visual Studio's official documentation uses the term functor as of 2021:
https://learn.microsoft.com/en-us/cpp/standard-library/funct...
A simple Google search shows no shortage of recent websites and documents including fairly authoritative references using the term functor to describe a type that overloads operator ().
Heck even the author of this article, Raymond Chen, uses the term functor as recently as 2020 to describe such a construct:
https://devblogs.microsoft.com/oldnewthing/20200513-00/?p=10...
Is Raymond Chen not a C++ expert?
The word "functor" has a long and glorious history in C++. Try entering "C++ Andrei Alexandrescu functors" into your internet search engine of choice. For bonus points, try "c++ Scott Meyers functor" as well.