You’ve seen it a thousand times today. It sits there on your keyboard, nestled between the "3" and the "E," or maybe you just tapped it to tag a photo of your lunch on Instagram. But if someone stopped you on the street and asked, "Hey, what is the name of the # symbol?" you’d probably hesitate. Is it a hashtag? A pound sign? A tic-tac-toe board?
Honestly, it’s all of those. And none of them.
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The history of this little grid is a mess of medieval shorthand, telephone engineering, and the sudden explosion of social media. It is one of the few characters in the ASCII set that suffers from a massive identity crisis. Depending on whether you are an accountant in London, a programmer in Silicon Valley, or a musician reading a lead sheet, the name changes completely.
The Most "Official" Name: The Octothorpe
If you want to win a pub quiz or sound like the smartest person in the IT department, you call it an octothorpe. It’s a weird word. It sounds ancient, maybe Greek or Latin, but it’s actually a product of 1960s corporate whimsy.
According to the most widely accepted history from Bell Labs, engineers were working on the new Touch-Tone dialing system. They needed a symbol to trigger specific functions on the telephone exchange. They chose the # and the *. While the star was easy to name (asterisk), the # was a bit of a blank slate.
Don Hoefler, a writer for the Bell Labs house organ, and several engineers—most notably Don McPherson and Howard Eby—decided "pound sign" or "number sign" wasn't technical enough. They coined "octothorpe." The "octo" part is obvious because the symbol has eight points sticking out. The "thorpe" part? That’s where things get murky. Some say it was named after the athlete Jim Thorpe. Others claim it was just a nonsense syllable added to make it sound official.
Regardless of its origin, the name octothorpe became the standard in telecommunications manuals. It’s the name used by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO). So, if you’re looking for the most "correct" technical term, that’s it. But good luck using it at a coffee shop without getting a blank stare.
Why Americans Call It the Pound Sign
Before it was a button on a phone, it was a unit of weight. This is where most people get confused. In the United States, if you ask "what is the name of the # symbol," the knee-jerk reaction is "pound sign."
This comes from a Latin abbreviation for libra pondo, which means "a pound by weight." Medieval scribes would write "lb" with a horizontal bar across the top (a tilde or a "scribal abbreviation") to show it was a unit of measure. Over centuries of messy handwriting and quick note-taking, that crossed-through "lb" morphed into the # we recognize today.
The British Conflict
In the UK, calling # a "pound sign" will lead to immediate confusion. For them, a pound sign is £, the symbol for their currency (Great British Pounds). If a Brit sees #, they almost always call it the hash. This distinction is vital in international business. Imagine an American telling a British developer to "hit the pound key" to reset a server. The Brit might go looking for the £ key on their specialized keyboard, while the American is wondering why nothing is happening.
The Rise and Dominance of the Hashtag
We can’t talk about the name of the # symbol without mentioning Chris Messina. In 2007, Messina walked into the Twitter offices (which were much smaller back then) and suggested using the # symbol to group related messages. He called them "channels."
The idea didn't stick immediately. Twitter’s founders actually told him it was too "nerdy" and would never take off. They were wrong.
The term "hashtag" is now so ubiquitous that younger generations don't even know it has other names. But linguistically, "hashtag" refers to the entire tag (the symbol plus the word), not just the symbol itself. If you write #Tech, the whole thing is the hashtag. The symbol is still technically the hash. However, in common parlance, the distinction has vanished. If you see a lone # on a billboard, people say "hashtag," and everyone knows what they mean.
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The Musical and Mathematical Side
Step away from the keyboard for a second. If you’re a musician, you look at # and see a sharp. Now, technically, a musical sharp ($\sharp$) is different. It has vertical lines and slanted horizontal lines, whereas the standard # has horizontal lines and slanted vertical lines. It’s a subtle tilt, but to a typesetter, it’s a world of difference.
In mathematics and programming, its identity shifts again.
- Number Sign: This is the most "plain English" version. It’s used to denote a rank, like #1.
- Crunch: In some old-school programming circles, particularly around the C programming language, it was occasionally called a "crunch."
- Mesh: Used in some early technical documentation.
- Gate: Because it looks like a garden gate.
In the C# programming language, the symbol is pronounced "sharp," following the musical theme. It’s meant to imply that C# is a step above the C++ language.
Why Names Actually Matter in 2026
You might think this is all pedantic, but naming conventions drive how we interact with technology. As voice-to-text and AI agents become the primary way we navigate the world, the name of the # symbol matters for accessibility.
If you tell a screen reader "octothorpe," it knows exactly what to do. If you say "number sign," it might interpret the context differently. When coding, using the wrong term in a "find and replace" or a script can break an entire database.
Furthermore, there is a certain cultural literacy involved. Knowing that the "hash" comes from "hatch" (meaning to cross-mark) or that the "pound" comes from "libra pondo" connects us to a timeline of human communication that stretches back hundreds of years. We aren't just using buttons; we are using evolved fossils of ancient handwriting.
The Practical Cheat Sheet
Since you likely won't remember every niche term, here is how you should actually refer to it based on who you are talking to:
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- With a Computer Scientist: Call it a hash or an octothorpe. They’ll appreciate the precision.
- In the UK or Australia: Always say hash. Avoid "pound" unless you want to talk about money.
- In the US at a Grocery Store: Use pound sign (e.g., "Enter your rewards number followed by the pound sign").
- On Social Media: Just say hashtag. Everyone else is.
- In Music Theory: It’s a sharp, but make sure you’re actually using the musical character $\sharp$ if you’re publishing a score.
Moving Forward with the
The symbol isn't going anywhere. It’s more powerful now than it was when it was just a shortcut for weight. It’s a tool for political movements, a way to categorize the entirety of human thought on the internet, and a vital part of every phone call you make to a customer service line.
Stop calling it "the tic-tac-toe thing."
The next time you’re setting up a password or tagging a post, remember that you’re interacting with a character that has survived the transition from physical ledgers to digital metadata. Whether you call it an octothorpe or a hashtag, you’re using a piece of history.
Actionable Next Steps:
- Check your keyboard settings: If you work internationally, see if your "US" vs. "UK" keyboard layout changes where the # symbol lives.
- Audit your digital accessibility: If you’re a developer or content creator, ensure your alt-text and screen-reader tests correctly identify the # symbol in the context you're using it (e.g., ensuring "hashtag" is read for social tags but "number" is read for rankings).
- Test your voice assistant: Try asking your phone to "type an octothorpe" and see if it recognizes the command. It’s a good way to see how updated your device's linguistic library is.