What do call this sign # - hash, pound sign, number sign or hashtag?
I think it can be all three, depending on the context.
It has several names. The most common is probably hash. In North American English, it’s sometimes called the pound sign and used as a symbol for pounds weight: this can be confusing for British people for whom a pound sign is £. It’s also known as the number sign in North American English, in contexts such as go to question #2 . In a musical context, the symbol is known as a sharp. The picturesque name octothorpe has also been introduced: it’s said to have been invented by an employee of Bell Laboratories in the 1960s, in honour of the American athlete Jim Thorpe (with the octo- part deriving from the symbol’s eight points). In the large form in which it appears on telephones it’s sometimes called a square.
Recently, the hash sign has acquired a new role. On social networking sites such as Twitter, it’s attached to keywords or phrases so as to identify messages on a particular topic (e.g. #volcano; #Iceland). These keywords or phrases are known as [hashtags] (Oxford Languages | The Home of Language Data). Oxford Languages | The Home of Language Data
What do you call this sign # - hash, pound sign, number sign or hashtag?
I personally usually refer to it as ‘hashtag’ although I know that this is not what it used to be called originally.
I call it the “pound sign” if there is not other context. Maybe from answering machines that always ask me to “press pound”.