flet

flet is a Lisp macro in `cl.el'.

(flet ((FUNC ARGLIST BODY...) ...) FORM...)

This macro is obsolete since 24.3;
use either `cl-flet' or `cl-letf'.

Make temporary overriding function definitions.
This is an analogue of a dynamically scoped `let' that operates on the function
cell of FUNCs rather than their value cell.
If you want the Common-Lisp style of `flet', you should use `cl-flet'.
The FORMs are evaluated with the specified function definitions in place,
then the definitions are undone (the FUNCs go back to their previous
definitions, or lack thereof).