Well, "passing off' is what the legal terminology is, I think. Basically, if my gran goes into a bookstore, sees seven books with HARRY POTTER AND THE ________________ and one that says HARRY POTTER LEXICON in the same font, then she's likely to be confused; that's "passing off". Remember way back when that first unauthorised HP companion book came out, and it was bright purple and didn't have the HP fonts or anything? That's why they did that, and I can't figure out why anybody thought doing it this way was okay.

Ditto.