Topics similar to or like first-class function

Technique for implementing lexically scoped name binding in a language with first-class functions. Record storing a function together with an environment. Wikipedia

Anonymous function is a function definition that is not bound to an identifier. Anonymous functions are often arguments being passed to higher-order functions, or used for constructing the result of a higher-order function that needs to return a function. Wikipedia

In computer science, the funarg problem refers to the difficulty in implementing first-class functions (functions as first-class objects) in programming language implementations so as to use stack-based memory allocation of the functions. Defined, but not in the environment of the function call. Wikipedia

Function which is defined within another function, the enclosing function. Itself invisible outside of its immediately enclosing function, but can see all local objects (data, functions, types, etc.) of its immediately enclosing function as well as of any function(s) which, in turn, encloses that function. Wikipedia

Entity which supports all the operations generally available to other entities. Argument, returned from a function, modified, and assigned to a variable. Wikipedia

Construct allowing an object to be invoked or called as if it were an ordinary function, usually with the same syntax . Function objects are often called functors. Wikipedia