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In engineering, a '''bug''' is a defect in the design, manufacture or operation of machinery, circuitry, electronics, [[Computer hardware|hardware]], or [[software]] that produces undesired results or impedes operation. It is contrasted with a [[glitch]] which may only be transient. Sometimes what might be seen as unintended or defective operation can be seen as a [[undocumented feature|feature]].

== History ==
The Middle English word ''[[wikt:bugge#Noun|bugge]]'' is the basis for the terms "[[wikt:bugbear#Noun|bugbear]]" and "[[wikt:bug-a-boo#Noun|bugaboo]]" as terms used for a monster.<ref>{{cite web |url= http://www.computerworld.com/article/2515435/app-development/moth-in-the-machine--debugging-the-origins-of--bug-.html |title= Moth in the machine: Debugging the origins of 'bug' |author= Computerworld staff |date= September 3, 2011 |work= Computerworld |url-status= live |archiveurl= https://web.archive.org/web/20150825040938/http://www.computerworld.com/article/2515435/app-development/moth-in-the-machine--debugging-the-origins-of--bug-.html |archivedate= August 25, 2015 |df= mdy-all }}</ref>

The term "bug" to describe defects has been a part of engineering jargon since the 1870s and predates electronic computers and computer software; it may have originally been used in hardware engineering to describe mechanical malfunctions. For instance, [[Thomas Edison]] wrote the following words in a letter to an associate in 1878:

{{blockquote|It has been just so in all of my inventions. The first step is an intuition, and comes with a burst, then difficulties arise—this thing gives out and [it is] then that "Bugs"—as such little faults and difficulties are called—show themselves and months of intense watching, study and labor are requisite before commercial success or failure is certainly reached.<ref name="Hughes1989">Edison to Puskas, 13 November 1878, Edison papers, Edison National Laboratory, U.S. National Park Service, West Orange, N.J., cited in  {{cite book |first= Thomas Parke |last=Hughes |title= American Genesis: A Century of Invention and Technological Enthusiasm, 1870-1970 |url= {{google books |plainurl=y |id=0r-ml88EynYC |page=75}} |year=1989 |publisher= Penguin Books |isbn= 978-0-14-009741-2 |page=75}}</ref>}}
This shows that using the word bugs was already widespread by 1870s.

In a [[comic strip]] printed in a 1924 telephone industry journal, a naive character hears that a man has a job as a "bug hunter" and gives a gift of a [[backscratcher]].  The man replies "don't you know that a 'bug hunter' is just a nickname for a [[repairman]]?"<ref>Cy Meyn, Hattie the Hello Girl, [http://bh.hallikainen.org/thg/monitor/Monitor_1924-01.pdf The Mountain States Monitor] Vol. XIX, No. 1 (Jan, 1924), Mountain States Telephone and Telegraph Co.; page 34, bottom.</ref>

[[Baffle Ball]], the first mechanical [[pinball]] game, was advertised as being "free of bugs" in 1931.<ref name="Baffle Ball">{{cite web |url= http://www.ipdb.org/machine.cgi?gid=129 |title= Baffle Ball |publisher= Internet Pinball Database |quote=(See image of advertisement in reference entry)}}</ref> Problems with military gear during [[World War II]] were referred to as bugs (or [[glitch]]es).<ref name="life1942062925">{{cite magazine |url= https://books.google.com/books?id=KlAEAAAAMBAJ&q=life%20magazine%20june%2029%201942&pg=PA25 |title= Modern Aircraft Carriers are Result of 20 Years of Smart Experimentation |magazine= Life |date= June 29, 1942 |accessdate= November 17, 2011 |page= 25 |url-status= live |archiveurl= https://web.archive.org/web/20130604220016/http://books.google.com/books?id=KlAEAAAAMBAJ&pg=PA25#v=onepage&q&f=true |archivedate= June 4, 2013 |df= mdy-all }}</ref> In the 1940 film, ''[[Flight Command]]'', a defect in a piece of direction-finding gear is called a "bug".{{citation needed|date=May 2019}} In a book published in 1942, [[Louise Dickinson Rich]], speaking of a powered [[ice cutting]] machine, said, "Ice sawing was suspended until the creator could be brought in to take the bugs out of his darling."<ref name="oclc_405243">{{Citation |last= Dickinson Rich |first= Louise |year= 1942 |title= We Took to the Woods |page= 93 |publisher= JB Lippincott Co |url= https://books.google.com/books?id=PT0zAQAAIAAJ |lccn= 42024308 |oclc= 405243 |postscript= . |url-status= live |archiveurl= https://web.archive.org/web/20170316164959/https://books.google.com/books?id=PT0zAQAAIAAJ |archivedate= March 16, 2017 |df= mdy-all }}</ref>

[[Isaac Asimov]] used the term "bug" to relate to issues with a robot in his short story "[[Catch That Rabbit]]", published in 1944.

[[File:First Computer Bug, 1945.jpg|thumbnail|250px|A page from the [[Harvard Mark II]] electromechanical computer's log, featuring a dead moth that was removed from the device.]]
The term "bug" was used in an account by computer pioneer [[Grace Hopper]], who publicized the cause of a malfunction in an early electromechanical computer.<ref>{{citation|title=FCAT NRT Test |publisher=Harcourt |date=March 18, 2008 |title-link=Florida Comprehensive Assessment Test }}</ref> A typical version of the story is:

{{blockquote|In 1946, when Hopper was released from active duty, she joined the Harvard Faculty at the Computation Laboratory where she continued her work on the [[Harvard Mark II|Mark II]] and [[Harvard Mark III|Mark III]]. Operators traced an error in the Mark II to a [[moth]] trapped in a relay, coining the term ''bug''. This bug was carefully removed and taped to the log book. Stemming from the first bug, today we call errors or glitches in a program a ''bug''.<ref>{{cite web |url=http://ei.cs.vt.edu/~history/Hopper.Danis.html |title=Danis, Sharron Ann: "Rear Admiral Grace Murray Hopper" |date=February 16, 1997 |publisher=ei.cs.vt.edu |accessdate=January 31, 2010}}</ref>}}

Hopper did not find the bug, as she readily acknowledged. The date in the log book was September 9, 1947.<ref>"[http://catb.org/jargon/html/B/bug.html Bug] {{webarchive|url=https://web.archive.org/web/20170323213836/http://www.catb.org/jargon/html/B/bug.html |date=March 23, 2017 }}", ''The Jargon File'', ver. 4.4.7. Retrieved June 3, 2010.</ref><ref name="si-bug">"[http://americanhistory.si.edu/collections/search/object/nmah_334663 Log Book With Computer Bug] {{webarchive|url=https://web.archive.org/web/20170323220950/http://americanhistory.si.edu/collections/search/object/nmah_334663 |date=March 23, 2017 }}", National Museum of American History, Smithsonian Institution.</ref><ref>"[https://web.archive.org/web/20000119173039/http://history.navy.mil/photos/images/h96000/h96566kc.htm The First "Computer Bug]", Naval Historical Center. But note the [[Harvard Mark II]] computer was not complete until the summer of 1947.</ref> The operators who found it, including William "Bill" Burke, later of the [[Naval Surface Warfare Center Dahlgren Division|Naval Weapons Laboratory]], [[Dahlgren, Virginia]],<ref>IEEE Annals of the History of Computing, Vol 22 Issue 1, 2000</ref> were familiar with the engineering term and amusedly kept the insect with the notation "First actual case of bug being found." Hopper loved to recount the story.<ref>{{cite web |author=James S. Huggins |url=http://www.jamesshuggins.com/h/tek1/first_computer_bug.htm |archive-url=https://web.archive.org/web/20000816023000/http://www.jamesshuggins.com/h/tek1/first_computer_bug.htm |url-status=dead |archive-date=August 16, 2000 |title=First Computer Bug |publisher=Jamesshuggins.com |accessdate=September 24, 2012  }}</ref> This log book, complete with attached moth, is part of the collection of the Smithsonian [[National Museum of American History]].<ref name="si-bug" />

The related term "[[debug]]" also appears to predate its usage in computing: the ''[[Oxford English Dictionary]]''{{'}}s etymology of the word contains an attestation from 1945, in the context of aircraft engines.<ref>''Journal of the Royal Aeronautical Society''. 49, 183/2, 1945 "It ranged ... through the stage of type test and flight test and 'debugging' ..."</ref>

=="It's not a bug, it's a feature"==
Some user bugs work as the designer intended, reflecting a mismatch between the specifications and user expectations. Sometimes the behavior in question is written in user documentation or is billed as an [[undocumented feature]], which is captured by the catchphrase "It's not a bug, it's a feature" (INABIAF).<ref name=wired>{{cite magazine|url=https://www.wired.com/story/its-not-a-bug-its-a-feature/|title='IT'S NOT A BUG, IT'S A FEATURE.' TRITE—OR JUST RIGHT?|magazine=Wired|author=Nicholas Carr}}</ref> This quip is recorded in [[The Jargon File]] dating to 1975 and may predate that. This reflects the programmer's humor to some extent.

==Types==
*[[Hardware bug]]
**[[hardware security bug|Security]]
*[[Software bug]]
**[[Firmware]]
**[[security bug|Security]]
**[[Microcode]]

==See also==
*[[Mutation|Genetic mutation]]

==References==
{{reflist}}

[[Category:Engineering concepts]]
[[Category:Engineering]]