Number sign facts for kids

The symbol # is often called the number sign, hash, or pound sign. People have used this symbol for many different things throughout history. For example, it can show an order (like #1 for "number one"). It also used to be a quick way to write "pounds" (like for weight), coming from an old symbol called ℔.

Since 2007, the # symbol became very popular on social media sites. People use it to create "hashtags" to tag topics. Because of this, the symbol itself is sometimes called a "hashtag."

The # symbol looks a bit like the sharp symbol (♯) in music or the equal-and-parallel symbol (⋕) in math. But you can tell them apart because the # has flat horizontal lines and vertical lines that tilt to the right.

The Story of the Hash Symbol

An old way to write "pound weight" in Latin, called libra pondo

Isaac Newton wrote this abbreviation, showing how the symbol changed from ℔ to #

Many people believe the # symbol started from an old Roman symbol: ℔. This symbol was a short way to write libra pondo, which means "pound weight" in Latin. Back then, they would print this symbol with a line across it. This was to make sure the letter "l" wasn't confused with the number "1." Over time, the symbol became simpler, looking like two horizontal lines "=" over two slanted lines "//." We know it was used to mean "pounds" as far back as 1850.

In 1853, a book about bookkeeping (keeping financial records) called the symbol the "number" character. By 1880, another bookkeeping book explained that it could mean two things. An instruction manual for the Blickensderfer model 5 typewriter from around 1896 seemed to call it the "number mark." Some early American books from the 1900s also called it the "number sign." A manual from 1917 explained its two main uses: "number" (when placed before a number) and "pounds" (when placed after a number).

The name "pound sign" for the # symbol started being used in the U.S. around 1932. Before that, and still in many places outside the U.S., the "pound sign" usually meant the currency symbol (£) or the weight symbol (lb). Some people thought the name "pound sign" came from early computer codes that used the same code for both the number sign and the British pound sign (£). However, its use for "pounds weight" in 1850 suggests it was used this way even before these codes.

The name "hash sign" started appearing in South Africa in the late 1960s and in other non-North American places in the 1970s.

The # symbol was mostly used when people wrote things by hand. In printing, other symbols like the numero (№) or barred-lb (℔) were used for "number" and "pounds."

The # symbol first appeared on the keyboard of the Remington Standard typewriter around 1886. It then became part of early teleprinter codes and later the ASCII computer code. This made it available on computers, leading to many new ways to use the symbol. In 1968, it was added to the bottom right button of touch-tone phone keypads. However, people didn't use this button much until voicemail systems became popular in the early 1980s.

How the Hash Symbol is Used in Computers

In the world of information technology (IT), the number sign often has a special meaning. Around 1988, it was used on IRC networks to label groups and topics. This idea inspired Chris Messina to suggest using a similar system on Twitter. He wanted to use the # symbol to tag topics on the microblogging site. While hashtags became most popular on Twitter first, their use quickly spread to other social media sites like Instagram, Facebook, Flickr, Tumblr, and Google+.

How the Hash Symbol is Used in North America

In the United States, when the # symbol comes before a number, it means "number." For example, "a #2 pencil" means "a number-two pencil." The only common exception is on a phone keypad. The # key on a phone is always called the "pound key." So, if you're told to dial #77, you would say "pound seven seven."

The # symbol is also commonly known as the "pound sign." When it comes after a number, it can mean weight in pounds.

In Canada, the symbol is called both the "number sign" and the "pound sign." Some phone systems even have an option for Canadian English, which makes the system say "number sign" instead of "pound sign" to callers.

How the Hash Symbol is Used in the United Kingdom and Ireland

In the United Kingdom and Ireland, the # symbol is usually called a hash. This name likely comes from "hatch," referring to cross-hatching (lines crossing each other). It is not used to mean pounds, either for weight (they use lb or lbs) or for money (they use "£" for pound sterling). It is also not called the "pound sign" there, as that term refers to the currency symbol "£" for the British pound.

People in Britain and Ireland might understand what "#" means as an abbreviation for "number" if they have dealt with American usage in business or school. However, you rarely see it used this way in print. British typewriters used to have "£" where American ones had "#." So, where Americans might write "Symphony #5," people in Britain and Ireland are more likely to write "Symphony No. 5."

Other Names for the Hash Symbol

The # symbol has several other names in English:

• Octothorp or Octothorpe: Many experts believe this word was created by workers at Bell Labs around 1968. They needed a name for the symbol on the telephone keypad. One story says Don MacPherson combined "octo" (meaning eight, because the symbol looks like eight spaces around a center) with the last name of Olympic athlete Jim Thorpe. Another story says Howard Eby and Lauren Asplund invented it as a joke in 1964. The word became popular inside and outside Bell Labs. The first time "octothorp" appeared in a U.S. patent was in 1973.

Images for kids

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  A close-up of a phone keypad showing the # symbol.

See also

In Spanish: Almohadilla para niños