A Ninja Typo is a punctuation or grammatical error that does not reveal itself to the author (no matter how
hard the author looks for it) until it is too late (i.e. after it has been published in a way that cannot be retracted).
Example : Dang! I proofread this email 3 times and I STILL managed to leave the “l” out of “turtle”. That Ninja Typo just killed my chances of getting re-elected.