The 'octothorpe' is better known as what on a keyboard?

The word octothorpe is beginning to appear in a few dictionaries, but still seems mostly to be a jargon term of the North American telephone business for the handset symbol #. It has reached semi-official status by being mentioned in international standards documents but that’s no guarantee of a wide circulation any time soon.

Octothorpe is just one of a plethora of names for the symbol. In the US it’s often called the pound key, because it has long been used to mark numbers related to weight, or for similar reasons the number sign, which is one of its internationally agreed names. Elsewhere it is commonly called hash, a term dating from the 1970s that may have been a popular misunderstanding of hatch.

Twitter documentation refers to it as "the hashtag symbol". The word "hashtag" is often used when reading social media messages aloud. For instance the text "#xyz" is often read out loud as "hashtag, x, y, z" (as opposed to "hash, x, y, z" or "number sign, x, y, z").