If You’ve Written A Typo Undetectable By Spellcheck, You’ve Created What?
Answer: An Atomic Typo
An atomic typo is a typographical error that is grammatically and/or contextually incorrect, but still spelled correctly–in other words, it’s what happens when you screw up a word so bad that you spell an entirely different word correctly.
Every time you type unclear instead of nuclear, damn instead of dam, or otherwise create a typo that yields a word which is correctly spelled but entirely the wrong one for your sentence, you’ve created an atomic typo.
The term was originally coined by C.F. Hanif, a Palm Beach Post editor, to refer to errors that resulted specifically from the transposition of letters (such as the reversal of the U and N in the unclear/nuclear error) but has since come to refer to any types that would be missed by spellcheck (regardless of whether they have a single letter transposition or not).