A Spelling Nazi is a subtype of Grammar Nazi, specializing in spelling. A Spelling Nazi would actively fight the Rouge Angles of Satin. A Spelling Nazi would make sure that "definately" was replaced by "definitely" and not "defiantly." A Spelling Nazi would always spell the names of the characters, settings, attacks, and MacGuffins in its fandom correctly if the correct spellings are known (and if they aren't, then expect those of different ideologies to try to tear one another's throats out over which is more "correct"). And God save us all if a British Spelling Nazi ever meets an American one.
This isn't necesessarily a bad thing. Like their relatives, the Grammar Nazis, Spelling Nazis often help correct mistakes throughout the wiki, keeping it easily legible. However, all these characteristics and a tendency for obsessiveness also makes them very easy to troll, which can easily escalate into a Flame War.