A typographical error (often shortened to typo) is a mistake made in the typing process (such as spelling) of printed material. Historically, this referred to mistakes in manual type-setting (typography). The term includes errors due to mechanical failure or slips of the hand or finger, but excludes errors of ignorance, such as spelling errors. Before the arrival of printing, the "copyist's mistake" or "scribal error" was the equivalent for manuscripts. Most typos involve simple duplication, omission, transposition, or substitution of a small number of characters.
The term fat finger, often in combination with "fat-finger syndrome", is used as slang to refer to the invocation of an unwanted secondary action due to one's finger being bigger than the envisioned touch zone, or accidental inaccuracy in the fine motor movements of one's extremities. In general terms, for example, pressing a different button than expected on a touchscreen, or hitting two adjacent keys on a keyboard in a single keystroke during data entry (for example, buckled instead of bucked due to the L key being next to the K key on many keyboards).
"Intentional" typos 
Certain typos, or kinds of typos, have achieved widespread notoriety and are occasionally used deliberately for humorous purposes. For instance, the British newspaper The Guardian is sometimes referred to as The Grauniad due to its reputation for frequent typesetting errors in the era before computer typesetting. This usage began as a running joke in the satirical magazine Private Eye. The magazine continues to refer to The Guardian by this name to this day.
Typos are common on the internet in chatrooms, Usenet and the World Wide Web and some, such as "teh", "pwned", and "zomg" have become in-jokes among Internet groups and subcultures. pron is not a typo but an example of obfuscation.
Typosquatting is a form of cybersquatting which relies on typographical errors made by users of the Internet. Typically, the cybersquatter will register a plausible typo of a well-known website address in hopes of receiving traffic when Internet users mistype that address into a web browser. Deliberately introducing typos into a web page, or into its metadata, can also draw unwitting visitors when they enter these typos in Internet search engines.
Typos in online auctions 
Since the emergence and popularization of online auction sites such as eBay, misspelled auction searches have quickly become a gold mine for deal hunters. The concept on which these searches are based is that, if an individual posts an auction and misspells its description and/or title, regular searches will not find this auction. However, a search which includes misspelled alterations of the original search term in such a way as to create misspellings, transpositions, omissions, double strikes, and wrong key errors would find most misspelled auctions. The resulting effect is that there are far fewer bids than there would be under normal circumstances allowing for the searcher to obtain the item for less. A series of third-party web sites have sprung up allowing people to find these items.
Marking typos 
When using a typewriter without correction tape, typos are commonly overstruck with another character such as a slash. This saves the typist the trouble of retyping the entire page to eliminate the error, but as evidence of the typo remains, it is not aesthetically pleasing.
In instant messaging, users often send messages in haste and only afterwards notice the typo. It is common practice to correct the typo by sending a subsequent message where an asterisk precedes or follows the correct word.
In formal prose, it is sometimes necessary to accurately quote text containing typos. In such cases, the author will write "[sic]" to indicate that an error was in the original quoted source rather than in the transcription.
Atomic typos 
Another kind of typo, informally called an "atomic typo," is a typo in a newspaper or magazine or blog post that is spelled correctly but used in the wrong way or context, and since it is spelled correctly, the spellchecker cannot find the mistake. Examples include unclear instead of nuclear, sedan instead of Sudan, add instead of ass, Governor Crist instead of Governor Christ. The term was coined in 2002 by Palm Beach Post editor C.F. Hanif.
- According to a note in St Mary's Church, Totnes, Devon, UK
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