Meaning of "Procedure-valued variable?

What does it meant by a 开发者_如何学Cprocedure-valued variable in the programming language context .

When a variable contains a procedure? Like in functional languages, where you can sth like:

variable f = new function(int x) { return x*2; } 
int i = f(3);

I've never heard this term. But from what I've gathered via google (e.g. http://thid.thesa.com/thid-0513-0671-th-1411-0895, http://comjnl.oxfordjournals.org/content/17/1/38.full.pdf), it seems a pretty obscure and old term for or variables of a "callback" or "function" type - a variable that contains a (kind of reference to a) function/procedure.

Most probably, a variable, the value of which is a procedure. Many modern programming languages support this notion. For example, C has function pointers:

void foo()
{
    printf("Hello, world!\n");
}

int main()
{
    void (*funcp)(void);  // pointer to function
    funcp = foo;
    funcp();
}

Python:

def foo():
    print 'Hello, world!'

f = foo  // assign foo (a function) to variable foo
f()