The approximate order of frequency of the most commonly used letters in the English language, ETAOIN SHRDLU is best known as a nonsense phrase that sometimes appeared in print due to a quirk of Linotype machines, which dominated publishing for a century until being replaced by computers. The complete sequence is ETAOIN SHRDLU CMFGYP WBVKXJ QZ.
ETAOINSHRDLU were the first 12 letters on the Linotype keyboard, which was arrayed in order of frequency of usage. Linotype operators often generated the phrase by running their fingers down the line of keys, in order to complete a slug of type that contained a mistake. Occasionally this erroneous type would be included in the printed publication.
That happened often enough that the phrase is listed in the Oxford English Dictionary and has been used as a character name by a number of authors, notably that of an irascible bookworm in Walt Kelly's comic strip Pogo. It was also used as the name of the computer program SHRDLU.
