7 Shocking Secrets Of The Pound Key (#) You Never Knew: From Telephone Button To Global Hashtag

As of December 2025, the humble symbol we call the "pound key" has undergone a complete identity transformation, evolving from a simple telephony function to the single most powerful tool for digital organization and social movements: the hashtag. This unassuming lattice of two horizontal and two vertical lines, officially known as the number sign, is a typographical chameleon whose name changes depending on where you are, who you're talking to, and what device you're using. Understanding its full history and its current, dominant role in the digital landscape is key to grasping modern communication. The journey of the symbol is a fascinating case study in technological evolution, having been repurposed multiple times across different eras—from abbreviating weight measurements to directing automated phone calls, and now, to categorizing billions of online conversations. It’s a symbol with an identity crisis, known by more names than almost any other character on your keyboard, a fact that speaks volumes about its enduring utility and adaptability in a rapidly changing world.

The Identity Crisis: A Complete List of Names for the # Symbol

The primary confusion surrounding the pound key stems from its sheer number of names. What you call it often depends entirely on your geographic location or your professional field. This multiplicity of names contributes significantly to its topical authority, linking it to various domains from telecommunications to programming and social media. Here is a comprehensive list of the most common names for the # symbol:

• Pound Sign / Pound Key: The most common name in the United States and Canada, primarily because the symbol was adopted by Bell Labs for the Touch-Tone telephone keypad in the 1960s. It was chosen to represent "lbs," the abbreviation for the unit of weight (pounds).
• Number Sign: The official, generic typographical name. It is traditionally used to indicate a number, as in "Apartment #5."
• Hash / Hash Mark / Hash Key: The prevailing term in the United Kingdom, Ireland, Australia, and many other English-speaking countries. When you are asked to "press the hash key," this is the symbol being referenced.
• Octothorpe: The most obscure and technical name. It is believed to have been coined by Bell Labs engineers in the 1960s when they were designing the Touch-Tone keypad, possibly combining "octo" (eight points) and "thorpe" (an old word for a village or field).
• Hashtag: The name given to the symbol when it is used on social media platforms like Twitter, Instagram, and TikTok to tag or categorize content. This is arguably its most famous and globally recognized name today.
• Sharp: In music notation, the symbol is used as a sharp sign, which raises a note by a semitone. While visually similar, the true sharp sign (♯) is technically different, but the pound key is often used as a substitute in plain text.
• Hex: A less common name, sometimes used in computing and programming contexts.

This long list of names illustrates the symbol's journey from a niche typographical mark to a universal digital signifier.

The Analog Origin: From Weight Abbreviation to Touch-Tone Keypad

The pound key's modern life began not on a computer screen, but on a telephone. The Pre-Digital Era: Long before the internet, the symbol was primarily used in North America as an abbreviation for the unit of weight, "pound," short for the Latin word *libra* (hence "lbs"). For example, a grocer might write "5# of apples." This is the historical reason why Americans call it the "pound sign." The Touch-Tone Revolution (1963): The symbol's true destiny was sealed when Bell Labs introduced the Touch-Tone telephone keypad in 1963. They needed two extra keys alongside the numbers 0-9 to handle new telephony functions. The asterisk (*) and the pound symbol (#) were chosen. Bell Labs officially designated the # key as the "pound sign" for their North American market. Early Telephony Uses: In the early days of automated voice response systems (IVR), the pound key became a crucial navigational tool. The common instruction, "Press the pound key to continue," or "Press the pound key to confirm your selection," established its function as an "enter" or "end of entry" command within the telephone system. This remains one of its core functions in automated phone menus today.

The Digital Revolution: How the Pound Key Became the Global Hashtag

The most significant and recent chapter in the pound key's history is its transformation into the "hashtag," a phenomenon that has fundamentally reshaped social media and digital communication. Programming and Computing Roots: Before social media, the symbol was already important in computing. In programming languages like C and C++, it is used as a preprocessor directive. In scripting languages like Python and Ruby, and in Unix shell scripts, it is used to denote a comment—anything that follows the '#' on a line is ignored by the computer. This established its function as a meta-data marker. The Birth of the Hashtag (2007): The term "hashtag" was coined in 2007 by Chris Messina, a former Google developer, who proposed using the pound symbol on Twitter to group related messages. His idea was to use it as a way to categorize and filter content, similar to how it was used in Internet Relay Chat (IRC) to label channels. The idea caught on, and by 2009, Twitter officially adopted the hashtag, making it clickable and searchable. The Modern Power of the Hashtag: Today, the hashtag is far more than a simple tag. It serves multiple, powerful functions:

• Topical Categorization: It allows users to find all discussions related to a specific event or topic, such as #Euro2024 or #ClimateAction.
• Social Movements: It has become a crucial tool for organizing and amplifying social and political movements, such as #BlackLivesMatter or #MeToo.
• Branding and Marketing: Companies use branded hashtags (e.g., #ShareACoke) to launch campaigns and track user-generated content.
• Virality and Trending: Hashtags are the mechanism by which topics "trend" globally, driving massive amounts of traffic and attention to current events.

This digital evolution has completely overshadowed its original use. For an entire generation, the pound key is simply the "hashtag key," a direct link to the pulse of global conversation.

Key Differences: Pound Sign vs. Hashtag vs. Sharp Sign

While the visual symbol remains the same, understanding the context is crucial to using the correct terminology and function. Pound Sign (#): This term should primarily be reserved for its use in North American telephony ("Press the pound sign") or as a numerical indicator ("See page #10"). It is a functional key on a phone or a typographical abbreviation. Hashtag (#): This term is reserved exclusively for its use on social media and digital platforms to tag, categorize, or create a searchable link. The moment you place the symbol before a word on a platform like Instagram, it transforms from a pound sign into a hashtag. Sharp Sign (♯): Although the pound key is often used as a substitute, the true sharp sign in music notation is technically distinct. The sharp sign has two vertical lines that are slightly slanted, whereas the pound sign's lines are perfectly vertical. However, in plain text communication, the pound key is the accepted substitute. The pound key, or the number sign, or the hash, or the octothorpe, is a perfect example of a symbol whose meaning is entirely defined by its context. Its longevity is a testament to its simple, yet effective, design, allowing it to transition seamlessly from the analog world of telephone wires to the digital universe of global social networking. Its latest chapter as the hashtag ensures its relevance for decades to come, proving that even the most unassuming keys on your keypad can hold immense power.