Dictionary: First Class Methods/Functions

In Programming language first class methods/functions means the programming language treats the method or function as a first class citizen. 

Based on Structure and Interpretation of Computer Programs 2nd Edition Book, elements with fewest restrictions are said to have first-class status. The rights and privileges  of first-class element are:

• They may be named by variables.
• They may be passed as arguments to procedures.
• They may be returned as the results of procedures.
• They may be included in data structures.

So if a language support a first-class function, it will let the functions to be passed as a parameters, and returned as a result of procedures. First class function is necessary for the functional programming style.

Example of programming languages that support first-class function are Scheme, ML, Haskel, F#, Perl, Scala, Python, PHP, Lua, JavaScript, C#, C++, and etc.

Sources:

1. http://en.wikipedia.org/wiki/First-class_function
2. Abelson, Harold; Sussman, Gerald Jay (1996). Structure and Interpretation of Computer Programs - 2nd Edition. MIT Press.