Number sign

Also called hash, pound sign, or octothorpe.

How to type it

Left middle finger with Shift.

Common uses

• In the United States, # before a numeral means number, as in #1 or apartment #4.
• On social media, # turns the word after it into a searchable hashtag.
• In the United States, the # key on a phone keypad is called the pound key.

Less common uses

• In shell scripts, Python, and many other languages, # starts a comment that the computer ignores.
• In CSS, # selects an element by its id, and in URLs # points to a section of a page.
• Chat apps such as Slack use # to refer to a channel.