Great question. Learning some etymology here would be helpful. The word Bible comes from Middle English via Old French, which ultimately comes from ancient Greek: biblia.
Biblia is the neuter plural of Biblion, which simply means book. Because Christianity created the book as we know it today (it was called a codex), the bible that we have today was called ta biblia to hagia, the holy books. So, today in common parlance, the bible is the Old and New Testaments, if you are from a Christian tradition. If you are from a Jewish tradition, then you would be referring to the Hebrew Scriptures.
If we step out into a non-religious sphere, the word bible would refer to any authoritative book. For example, the grammar bible would be an authoritative grammar book.
In short, within a religious tradition, the bible is a holy book; in a secular tradition, the bible is any authoritative book.