Atos, it was and still is clear, I wasn't referring to your post directly. In any case one game being in one database doesn't make it book as has been said ad nauseam. I guess we need to know where the chess.com computerised analysis gets its "book move" criterion from.
It needn't to be said ad nauseam, or at all, as far as I am concerned.
The database that is the engines opening library is commonly known as a book. The engine refers to it as a book move. How hard is it to understand that vocabulary. It is also easily understood.
Now, a portion of book moves, engine vocab or otherwise always get outdated or bugged. Time will tell. It should be reported to staff that the book now used by their analysis engine has this error. There will always be errors so book moves should always be measured against fresh analyis.
The vocabulary is perfectly simple. This is my trouble though. I get nearly all my games on chess.com analysed by the chess.com computer; sometimes this is good, sometimes it has holes as has been pointed out in other forums. What is not perfectly simple to me is this: in many of those games the chess.com stops referring to moves as "book moves" quite early on in well known lines which are in many books and most databases and of which there are many examples, therefore according to what you are saying I have to assume that not one of these games in these various lines are in the chess.com computer's opening "book" (there's that word again, what does it mean I wonder). On the other hand a poor move which to date has only been shown in one game in one database is indeed part of its book. This beggars belief.
Atos, it was and still is clear, I wasn't referring to your post directly. In any case one game being in one database doesn't make it book as has been said ad nauseam. I guess we need to know where the chess.com computerised analysis gets its "book move" criterion from.