A ninja edit is an change made to a published post or article (typically on a bulletin board) that preempts the first response made. Often, the existence of the ninja edit is only made clear by a reference to the mistake or inconsistency in the original article by the response. In such a case, the author of the response began writing before the ninja edit, but submitted the response after the ninja edit had been made.

The phrase is made up of ninja, a much-revered warrior caste famed for their speed and agility, and edit, the process of changing a creative work.

The usefulness of ninja edits is typically hightened by bulletin boards that allow free editing of a post before any responses have been made, but make a mandatory note of any edits made after the first response has been made. Hence, if the author identifies the mistake, he or she must act quickly to rectify it before another poster replies.
Original post by X:
Hey! I had a really fun day today, I went to the beach with my boyfriend.

Y reads the original post.

X then edits the post to read:
Hey! I had a really fun day today, I went to the beach with my girlfriend.

Meanwhile, Y has written, and subsequently entered, the post:
HAHA! You have a boyfriend? j00r a fag!

Y then reads the edited original post, then enters the post:
Oh! Nice ninja edit!

In this case, the thread would read, to a party reading it at a later time:

X: Hey! I had a really fun day today, I went to the beach with my girlfriend.

Y: HAHA! You have a boyfriend? j00r a fag!

Y: Oh! Nice ninja edit!
by Odiumjunkie February 28, 2006
Get the ninja edit mug.
A ninja edit that took too long to write (typically over one minute). In common with ninja edits, no confusion results from changed contents, but *edit star shows up, bringing with it uncertainty and dread.
Herp derp ah totally agree with the parent derp.
*(lazy ninja edit)
by a redditor November 28, 2010
Get the lazy ninja edit mug.