Why can I use double-quotes around "count" but not "least"?

I don't understand why these functions behave differently. The fact that they have a different arity shouldn't affect my ability to quote them.

janus@janus-ux305ca ~ % psql
psql (14.11 (Debian 14.11-1.pgdg110+1))
Type "help" for help.

janus=> select least(1,2);
 least 
-------
     1
(1 row)

janus=> select "least"(1,2);
ERROR:  function least(integer, integer) does not exist
LINE 1: select "least"(1,2);
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
janus=> select "count"(1);
 count 
-------
     1
(1 row)

What is the correct terminology that explains the difference in behaviour?