>> A good explanation is in (info "(emacs) Defining Abbrevs"):
>>
>>      ‘C-x a i g’ (‘inverse-add-global-abbrev’) and ‘C-x a i l’
>>   (‘inverse-add-mode-abbrev’) perform the opposite task: if the abbrev
>>   text is already in the buffer, you use these commands to define an
>>   abbrev by specifying the expansion in the minibuffer.  These commands
>>   will expand the abbrev text used for the definition.
>
> If you like what the manual says, why not say in the doc string what
> the manual says, or some simple variant of that?  I doubt that you'll
> be able to come up with a significantly shorter description that is
> still clear enough.

So here it uses the text copied from the manual: