— Macro: cl-flet (bindings...) forms...

This form establishes let-style bindings on the function cells of symbols rather than on the value cells. Each binding must be a list of the form ‘(name arglist forms...)’, which defines a function exactly as if it were a cl-defun form. The function name is defined accordingly for the duration of the body of the cl-flet; then the old function definition, or lack thereof, is restored.

You can use cl-flet to disable or modify the behavior of functions (including Emacs primitives) in a temporary, localized fashion. (Compare this with the idea of advising functions. See Advising Functions.)

The bindings are lexical in scope. This means that all references to the named functions must appear physically within the body of the cl-flet form.

Functions defined by cl-flet may use the full Common Lisp argument notation supported by cl-defun; also, the function body is enclosed in an implicit block as if by cl-defun. See Program Structure.

Note that the cl.el version of this macro behaves slightly differently. In particular, its binding is dynamic rather than lexical. See Obsolete Macros.

— Macro: cl-labels (bindings...) forms...

The cl-labels form is like cl-flet, except that the function bindings can be recursive. The scoping is lexical, but you can only capture functions in closures if lexical-binding is t. See Closures, and Using Lexical Binding.

Lexical scoping means that all references to the named functions must appear physically within the body of the cl-labels form. References may appear both in the body forms of cl-labels itself, and in the bodies of the functions themselves. Thus, cl-labels can define local recursive functions, or mutually-recursive sets of functions.

A “reference” to a function name is either a call to that function, or a use of its name quoted by quote or function to be passed on to, say, mapcar.

Note that the cl.el version of this macro behaves slightly differently. See Obsolete Macros.