It looks like there are actually three kinds of no-op functions.
* doc/lispref/functions.texi (Calling Functions): Fix count and
plural of no-op functions.
Copyright-paperwork-exempt: yes
(cherry picked from commit
99efe5c80f9d90de6540ef6f78504c0413947a25)
that accept function arguments are often called @dfn{functionals}.
Sometimes, when you call a functional, it is useful to supply a no-op
-function as the argument. Here are two different kinds of no-op
-function:
+function as the argument. Here are three different kinds of no-op
+functions:
@defun identity argument
This function returns @var{argument} and has no side effects.