Etaoin shrdlu

Etaoin shrdlu (, ) is a nonsense phrase that sometimes appeared in print accidentally in the days of "hot type" publishing because of a custom of type-casting machine operators to fill out and discard lines of type when an error was made. It appeared often enough to become part of newspaper lore – a documentary about the last issue of "The New York Times" composed using hot metal (2 July 1978) was titled "Farewell, Etaoin Shrdlu" – and "etaoin shrdlu" is listed in the "Oxford English Dictionary" and in the "Random House Webster's Unabridged Dictionary".
It is the approximate order of frequency of the 12 most commonly used letters in the English language.
History.
The letters on type-casting machine keyboards (such as Linotype and Intertype) were arranged by descending letter frequency to speed up the mechanical operation of the machine, so lower-case codice_1 and codice_2 were the first two columns on the left side of the keyboard.
Each key would cause a brass 'matrix' (an individual letter mold) from the corresponding slot in a font magazine to drop and be added to a line mold. After a line had been cast, the constituent matrices of its mold were returned to the font magazine. 
If a mistake was made, the line could theoretically be corrected by hand in the assembler area. However, manipulating the matrices by hand within the partially assembled line was time-consuming and presented the chance of disturbing important adjustments. It was much quicker to fill out the bad line and discard the resulting line of text, then redo it properly. 
To make the line long enough to proceed through the machine, operators would finish it by running a finger down the first columns of the keyboard, which created a pattern that could be easily noticed by proofreaders. Occasionally such a line would be overlooked and make its way into print.
Appearances outside typography.
The phrase has gained enough notability to appear outside typography, including: