You type it constantly. You call it the hashtag, and you probably have for years now, without a second thought. But that little symbol has led a long and surprisingly tangled life, and “hashtag” is only its most recent name. It has been called at least four different things over the years, and some of them are much stranger than others.
The symbol is far older than social media, older than the internet, older than the telephone. It picked up new names as it moved through different corners of the world, and it never fully shed the old ones. So let us actually meet it properly.
The one nobody expects: the octothorpe
Here is the name that stops people in their tracks. Some engineers call it the octothorpe. It is a genuinely odd word, and the story behind it is just as odd. It may have been invented as a bit of a joke at Bell Labs back in the nineteen sixties, cooked up by the people working on telephone systems.
The “octo” part is easy enough, a nod to the eight points sticking out around the edges of the symbol. Count the little ends and you get eight. The “thorpe” part is where things get murky, and the exact reasoning has been lost or muddied by decades of retelling. What is clear is that it started as insider telephone-lab lingo and somehow survived as a real, if rarely used, name.
Most people go their whole lives without ever hearing “octothorpe.” Drop it into conversation and watch faces change. It is the secret formal name of a symbol everyone uses and almost no one can name correctly.
Pounds, weights, and the phone in your pocket
Long before any of the modern names, the symbol was practical shorthand. It started as a way to write pounds, as in the unit of weight. That is a big part of why, for decades, people in the United States called it the pound sign. When an automated phone system told you to “press the pound key,” this is the symbol it meant.
It also spent a long stretch as the number sign, used to mark a quantity, as in writing it before a figure to mean “number.” So depending on where you were and what you were doing, the exact same symbol was a weight, a number, or a button on your phone. It quietly wore three different hats at once, and which name you used said a lot about your line of work.
None of these meanings ever really disappeared. They just piled up on top of each other, one symbol accumulating job after job across weights, quantities, and telephones, waiting for its biggest role yet.
How “hashtag” took over the world
Then came the moment that changed everything. In two thousand seven, a designer suggested using the symbol on Twitter as a way to group related posts together. Put it in front of a word, and suddenly you could bundle every message about the same topic into one searchable stream. It was a small idea that turned out to be enormous.
That single suggestion gave the symbol its newest and now most dominant name. The word “hashtag” took over so completely that an entire generation knows the symbol by nothing else. The pound sign, the number sign, the octothorpe, all of it got quietly overwritten in everyday speech by a name that did not even exist before social media.
We love this arc when we build apps and tools, because it is a perfect example of how a tiny design decision can completely redefine something that already existed for centuries. Nobody invented the symbol for Twitter. They just gave an old, overloaded character one more job, and that one job rewrote its entire identity. The tech we build on is stacked with history like this, and the humble hashtag, with its four names and its centuries of baggage, might be the best story of the bunch.
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