When talking about the Bible, most people divide it up into two sections that they call the New Testament and the Old Testament. There are correct ways to divide the Scriptures, but this isn’t one of them.
First of all, the Old and New Testaments refer to covenants, not to books or to collections of writings (in fact, much of what we know about the New Testament or New Covenant is found in the part of the Bible most call the Old Testament). A better way to refer to these sections in the Bible are the Hebrew Scriptures and the Greek Scriptures, based on the languages they were written in.
A second, equally valid way to divide the Bible, a way that few seem to be familiar with anymore, is between the 13 epistles written by the apostle Paul and the rest of Scripture. Paul came to bring Gentiles the Gospel of the Uncircumcision, while nearly all of the rest of the Bible (aside from parts of Acts) proclaims (or at least builds up to) the Gospel of the Circumcision, so a good way to label this division in the Bible is the Circumcision writings and the Uncircumcision writings. If you’re not familiar with this particular division, I write about it in depth in chapter 1 of my book titled Nearly everything we learned at church was wrong: What the Bible actually teaches about sex, hell, tithing, and much more.
I should also add that calling the Hebrew Scriptures the Old Testament is also somewhat antisemitic. Among other things, it implies that both the Hebrew Scriptures and the Mosaic law are not important or even still relevant. While the Old Testament or Covenant won’t remain relevant forever (both the Hebrew and Greek Scriptures tell us that the New Covenant will eventually come fully into effect), and is even now ready to vanish, the Old Covenant and the Mosaic law are still in effect for Israel right now (at least in part). And the Mosaic law itself (which is what most people think of when they think of the term “the Old Testament”) won’t end for at least 1,000 years after the Old Covenant fully fades away and the New Covenant begins in earnest (at the beginning of the Millennial Kingdom). Yes, at the end of the Millennium, when the heavens and Earth pass away and a new heaven and Earth are created, the Mosaic law will have served its purpose, but at this point in time both the Mosaic law and Old Covenant are still both here, at least for Israel.