In the section 2.1 "Printed Representation and Read Syntax" (https://www.gnu.org/software/emacs/manual/html_node/elisp/Printed-Representation.html), word "hash notation" is used to refer to the symbol "#".
But it may well confuse non-native English speakers, because the "hash" is also associated with "hash function".

A better name for "#" is "number sign".