Detail explanation and thank you for that ..
Let me try to conclude it shortly, hope will be correct conclussion.

All books are called bibble, as bibble is devided into two : Old and New Testament, and the New Testament is four books of gospel. So when we say bibble it refers to books in general ( it can be Old Testamen or New one), but when we say gospel it must be referring to only four last books.

Is it correct bro?