-Its basically someone who can't accept criticism of his or her series/game. Its more common in CoD fans or such, but you'll tend to find a good amount in big 3 fans as well. The most common thing this refers to in video games is "the developer is always right", a kind of defense that resembles "well they intended for that" in game design or execution.
+Explained it to you so you didn't cop out on lazyness.
Being a gamer and all I see this behavior all the time. Its quite silly frankly and especially so for video games because there are obvious bugs/gliches that when mentioned get the wk's involved in actually defending broken code. Even when asking for help you get people defending the game instead of helping, or refusing to admit that certain things are ridiculously broken in equality and continuing to abuse game mechanics or gliches with the excuse that the devs are always right.
In anime its more often about how an author fucks with its readers in order to gain more profit/prolong the series. As many current anime/manga fans of the big three rarely read a series not done weekly or with a considerably shorter volume set, it never really occurs to them that the writer would ever do something like make unnecessary arcs. (This happens all the time with longer shone, such as One Piece, Bleach, even Hunter x Hunter, hell even berserk).
The white knights come in when anything is mentioned on such topic and they defend it regardless of whether its true or not. There are countless examples of when an author just puts out chapters just for the sake of publication, regardless of plot relevance or starts a ridiculously irrelevant arc such as:
-One Piece: New Fishman Pirates
-Naruto: Fourth War
-Hunter x Hunter: Video Game arc.
-Berserk: Mermaid/reality change arc.
-Sun-Ken Rock: Idol arc.
I really could go on for pretty much every series, but generally the point is that there is an arc in every anime that "relates" to the other arcs but isn't really relevant or important to the final outcome of the series.