number sign; hash sign; pound sign
Refers to the symbol #, used in contexts such as phone menus, social media hashtags, or numbering. In Japanese, it is often called シャープ (sharp) in music or 井桁 (igeta) for the shape, but ナンバーサイン is used for the symbol in computing/telephone contexts.
Please enter the number sign after the phone number.
Using the hash sign on social media makes it easier to find posts on the same topic.