txt refers to the English language slang used on mobile phone short message services. It is an abbreviated form of English, similar to leet, but without the script kiddie content. Another example of this is AOL speak.
Txt includes some of the old standbys of using letters (r, u, b, c) as a rebus in place of entire words (such as "are", "you", "be" and "see"). It also retains the use of numerals to shorten text: 2 can do double-duty for "to" and "too", while 4 represents the word "for" as well as the syllable "for" at the beginning of words (4get). "Before" becomes "b4" turning both symbols into singular characters. The numeral 8 represents the "8" sound at any place in a word: sk8, gr8, vac8ion, sk8er, hesit8, w8ress, 8ypical.
.txt is an extension on computer file names for files that consist of plain text without bolding, italics, underlining or special colors or graphics. Files with the .txt extension can easily be read or opened by any program that reads text. See Binary and text files.