- Also called:
- hash sign, hash mark, pound sign, or octothorpe
number sign
-
What is the number sign symbol?
The number sign, or hashtag, is a symbol (#) with diverse applications across mathematics, computing, and medicine.
Originating from the Latin libra pondo, meaning "a pound weight," it evolved from the abbreviation lb with a bar across the top.
Commonly used to abbreviate the word "number" (e.g., "#2 pencil") or to number lists, it precedes the number it labels. In telecommunications, it's known as the pound sign or octothorpe. The prefix octo- refers to the eight points on the symbol, but the -thorpe stem defies explanation.
In the 21st century, the number sign introduces a hashtag, a digital tag that inscribes keywords as metadata and facilitates the categorization and organization of digital content by topic.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What does the number sign look like?
The number sign, or #, is a versatile symbol with various applications. It is commonly used to preface numbers (e.g., apartment #1). The number sign is also known as the pound sign or octothorpe.
Its origins can be traced to the Latin term libra pondo, meaning "a pound weight." The abbreviation "lb" evolved into the modern symbol #.
In the digital age, the number sign introduces a hashtag, a digital tag that categorizes online content. This use began on Twitter in 2007 and has become a tool for marketing and activism, seen in movements like #MeToo and #BlackLivesMatter.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some common names for the number sign?
The number sign, or #, has several common names. It is frequently called the number sign, especially in the United States, and is used to denote numbers, such as in "#2 pencil". It is also commonly referred to as the pound sign, particularly in telecommunications, where it is one of the standard keys on a telephone.
Another name for the number sign is octothorpe (sometimes spelled octothorp), a term that emerged when the telecommunications industry adopted the symbol for Touch-Tone dialing in the 1960s. In the context of social media, the number sign is known as the hash symbol, introducing hashtags that categorize digital content. Some believe the term hash may be related to the art technique called "hatching".
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How is the number sign used to indicate numbers?
The number sign, or hashtag, is a symbol (#) that is commonly used to precede numbers. In daily life, it is used to abbreviate the word "number," such as in "#2 pencil," or to number lists. In these instances, the number sign always appears before the number it labels. Less commonly, the number sign is used to refer to avoirdupois weight, in which case it appears after the number of pounds, such as in "2# bag of sugar".
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How is the number sign used on social media platforms?
The number sign, or hashtag, is used on social media platforms to categorize content and help users find topics of interest. A hashtag is a metadata label, which starts with the hash symbol (#) followed by a word or phrase with no spaces or punctuation. After a hashtag is posted, it becomes a hyperlink that leads to related content.
Hashtags are used in marketing campaigns and to bring awareness to social movements. For example, #BlackLivesMatter and #MeToo promoted social movements, while #MyCalvins (Calvin Klein) and #PutACanOnIt (Red Bull) promoted products.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some other uses or meanings of the number sign in language and technology?
The number sign, or #, has diverse applications across various fields. In everyday use, it abbreviates the word "number" (e.g., "#2 pencil") and is used to number lists. In this context, it precedes the number it identifies. It can also denote avoirdupois weight, in which case it follows the number of pounds (e.g., "2# bag of sugar").
In telecommunications, the number sign is one of two standard telephone keys, often called the pound sign or octothorpe. It gained prominence in the digital age as the symbol introducing a hashtag, which categorizes digital content on social media. This use began on Twitter in 2007 and has become a tool for marketing and activism, seen in movements like #MeToo and #BlackLivesMatter.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
number sign, versatile symbol (#) most commonly used to preface numbers (e.g., apartment #1) but which encompasses a variety of other uses, especially to tag (or hashtag) posts and messages on social media platforms.
Names
The origin of the number sign is usually attributed to the Latin term libra pondo, meaning “a pound weight.” This term was commonly abbreviated to lb (for libra), leading to the modern usage of the abbreviation for the unit of avoirdupois weight. Centuries ago the two letters lb were commonly written in English usage as ℔, a ligature that connects the letters with a bar across the top. Quick handwritten use of this symbol presumably morphed into the modern sign #.
Some have challenged this theory of the symbol’s origin, noting a lack of direct evidence for that evolution. Instead, some scholars suggest that the number sign arose independently and became conflated with the symbol for the pound sterling with the advent of telecommunications in the 19th century. This theory proposes that one version of the Baudot Code for the telegraph assigned the number sign (#) and the pound sign (£) to the same pattern of keystrokes, leading both to be referred to as the “pound sign.”
" height="20" alt="HEW Logo">
Also obscure is the coinage and derivation of the word octothorpe (also spelled octothorp) after the symbol was adopted for Touch-Tone dialing (see Telephone: Push-button dialing) by the telecommunications industry in the 1960s. It seems clear that the octo- (“eight”) prefix of the word refers to the eight points on the symbol, but the -thorpe stem defies easy explanation. One improbable theory holds that it is derived from the name of legendary athlete Jim Thorpe, although why that name should relate to the symbol is not explained. Another unexplained theory suggests that the stem is more properly rendered -thorp and derives from an Old English word for “village.” A third claim asserts that a Bell Labs employee simply burped while talking about the symbol and the resulting name stuck.
The use of the word hash to refer to the number sign may relate to the art technique called “hatching,” in which lines are used in close proximity to shade a picture. The sign itself resembles cross-hatching, a form of hatching in which two series of parallel lines intersect. However, this origin too has been disputed.
Uses
The number sign has a wide variety of uses across several different domains, including mathematics, computing, and medicine. In daily life it is commonly used to abbreviate the word number, as in “#2 pencil,” or to number lists. In these uses it always appears before the number it labels. Less commonly, it is used to refer to avoirdupois weight. In this case it appears after the number of pounds, as in “2# bag of sugar.”
It is also one of two symbols used as a standard telephone key, along with the asterisk (*). In this context it is typically called the pound sign but is sometimes referred to as the number sign or octothorpe. This key is not a part of standard phone numbers but is often used in voice-mail systems or automated phone systems.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
The use of the number sign in telecommunications transformed further with the rise of the computer age and the birth of the Internet in the late 20th century. In the 21st century the symbol commonly introduces a hashtag, a digital tag that inscribes keywords as metadata and facilitates the categorization and organization of digital content by topic. This specific usage began after it was proposed by a Twitter user in 2007 as a way to group tweets together. The feature allowed users to follow and participate in conversations surrounding trending topics and made hashtags a ubiquitous tool for marketing and activism. Among the notable campaigns fueled by hashtags are the #MeToo and #BlackLivesMatter movements.