Hashtag Symbol # — Meaning, History & All Its Names
The # symbol is everywhere — hashtags on social media, pound signs on phone keypads, number signs in writing, sharp signs in music. It has more names than almost any other symbol and a history that spans centuries. Here's the complete story.
What Is the # Symbol Called?
The # symbol has many names, which reflects how many different roles it plays:
- Hashtag: When used on social media to categorize posts (#travel, #food)
- Pound sign: Used in the US for the pound weight unit and on phone keypads
- Number sign: Used to indicate a number — #1, #10, Room #5
- Hash: Used in the UK and computing contexts
- Octothorpe: Technical name, used in telecommunications
- Sharp: In music, # raises a note by a semitone
- Space mark: In proofreading, # means "insert space here"
The History of the # Symbol
The # symbol's origin is debated among historians, but the most common theories trace it to:
Medieval Latin abbreviations: The abbreviation "lb" for libra (the Latin word for pound/balance) was written in a stylized way in medieval manuscripts. Over time, the intertwined "lb" letters gradually evolved into the # shape through changes in handwriting conventions.
Typographical evolution: By the 17th and 18th centuries, the # appeared in English typing and typesetting as a standard character on the keyboard. It appeared in early typewriters as the shift character on the 3 key.
The Octothorpe: A Name with a Mystery
The name "octothorpe" was coined in the 1960s or 70s by employees at Bell Telephone Laboratories when designing the touch-tone telephone keypad. The "octo-" refers to the eight points of the symbol. The "thorpe" part is debated — some say it was added arbitrarily, others claim it refers to Jim Thorpe (the athlete) who Bell Labs workers admired.
The octothorpe name remains primarily a technical and telecommunications term. Most people have never heard it, but it's the "official" name in many technical standards.
How the # Became the Hashtag
The transition from obscure keyboard character to cultural phenomenon happened in 2007. On August 23, 2007, web developer Chris Messina tweeted: "how do you feel about using # (pound) for groups. As in #barcamp [msg]?" — proposing to use # to organize Twitter posts into topic groups.
Twitter initially resisted the idea, but users adopted it organically. After the 2007 San Diego wildfires, #sandiegofire became a major way people organized information — and Twitter formalized hashtag support in 2009.
Instagram, Facebook, TikTok, LinkedIn, and virtually every other social platform followed, making # one of the defining symbols of social media culture.
How to Type the # Symbol
# in Music — The Sharp Sign
In Western music notation, # is used as a shorthand for the sharp sign ♯. When you see "C#" you read it as "C sharp" — a pitch one semitone above C. However, the proper musical sharp is ♯ (U+266F), which is slightly different in shape from the keyboard # (U+0023).
In song titles, chord charts, and informal music writing, # is used interchangeably with ♯ because it's easier to type. Professional sheet music uses the proper ♯ symbol.
# in Programming
The # has several important roles in programming:
- Python, Ruby, Shell: # begins a comment — everything after it is ignored by the interpreter
- C/C++: #include, #define, #if — preprocessor directives
- URLs: The # separates the URL from the anchor/fragment: page.html#section2
- CSS: # precedes hex color codes (#FF0000) and ID selectors (#header)
- Markdown: # creates headings — one # for h1, ## for h2, etc.
- GitHub: #42 references issue or pull request number 42
# as a Number Sign
In North America, # placed before a numeral means "number": #1 (number one), Room #5, Issue #42. This usage is more common in informal American English. In formal writing, "No." is preferred — No. 1, No. 5.
In other parts of the world, the # is not used as a number sign, which can cause confusion in international contexts.
Related Symbols
Fun Facts About the # Symbol
- The # key appears on virtually every keyboard ever made in the modern era
- The first hashtag #barcamp was used in 2007 — just 19 years ago
- In 2014, the word "hashtag" was added to the Oxford English Dictionary
- The # symbol has eight points — hence "octo" in octothorpe
- On UK keyboards, the # key is sometimes replaced by the £ (pound sterling) key, and # is accessed differently
- The American pound sign (#) and British pound sign (£) evolved separately for different historical reasons
Hashtag Best Practices
If you're using # for social media:
- No spaces: #travel works, #my travel doesn't
- Case doesn't matter: #TravelTips and #traveltips are the same
- Capitalize for readability: #BlackAndWhitePhotography is easier to read than #blackandwhitephotography
- Don't overdo it: Instagram recommends 3-5 relevant hashtags; Twitter 1-2
- Be specific: #food reaches everyone; #VeganRecipesForBeginners reaches your actual audience