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Bonus Facts:

• If you’re wondering why the symbol was called “hashtag” in the first place, the generally accepted name of the # symbol when referring to computer programming usage (often used as a comment sign, particularly in scripting languages), is “hash”. So in social media when tagging something using the hash sign, it was natural to call the grouping of the symbol with a tag a “hash tag”. This has since extended to the symbol itself sometimes being called this.  As for the first documented instance of someone calling such a tag “hash tag”, it appears to have been in an August 26, 2007 blog post by “Web Anthropologist” Stowe Boyd, titled “Hash Tags = Twitter Groupings“.
• An international standards body officially named the # symbol “square” in 1989.  This is why the British Post Office and British Telecom call the symbol a square.
• The # symbol is also commonly called a “sharp” in such places as Japan and others.  In many places, this is as a result of the similarity to the musical sharp symbol (♯).
• In the U.S. patent in 1973 where “octothorpe” first appears, the asterisk (*) was referred to as a “sextile”.
• Microsoft’s programming language C♯ (pronounced C-sharp) was once often mispronounced “C hash” or “C pound”.  The confusion comes from the fact that the symbol following the C is supposed to be the musical sharp symbol (♯). But given the # symbol’s prevalence in various programming languages, many programmers initially thought it was meant to be the “hash” symbol, until corrected.
• In Malaysia, the # symbol is commonly called a “hex”.
• In scripting languages where a # is followed by a ! (as in #!), this is known as a “shabang” (sometimes spelled “sh-bang” or “shebang”) and is typically used to tell the operating system what program to use to run some script.  The former name of “shabang” is thought to have come from the contractions “SHArp bang” or “haSH bang”; another popular theory is that it comes from the fact that the default shell “sh” is usually invoked with “shebang”, hence “sh-bang” and eventually “shabang”.  The latter “bang” name for the exclamation point is traditional Unix jargon.
• In Chess notation, the # symbol placed after a move indicates a checkmate.  This replaced the more traditional ‡ symbol.
• The compound tone generated on a phone by pressing the # key is a mixing of 941 Hz and 1477 Hz.