An acronym which stands for "
Auto-Correct Fail".
Used to describe the often-annoying Auto-Correct feature on many smartphones. Unless prevented otherwise, the Auto-Correct feature may choose to transform the word completely, thus rendering the phrase
nonsensical. In such situations, the victim often
can't be bothered to re-type the corrected sentence and an added apology. This can be rectified, excuse-free, by typing "ACF" followed by your originally intended phrase.