Understand that the ten sefirot Keter, Ḥokhma, Bina, Tiferet, and Malkhut are called by many names in the Book of the Zohar, in accordance with their numerous functions. When they are called Keter, Atzilut, Beria, Yetzira, and Asiya, their function is to distinguish between the vessels of the front, which are called Keter and Atzilut, i.e., Keter and Ḥokhma, and the vessels of the back, which are called Beria, Yetzira, and Asiya, that is, Bina, Tiferet, and Malkhut.
This distinction emerged among them through the combination of the attribute of judgment with the attribute of mercy.51As stated in the Petiḥa LeḤokhmat HaKabbala, section 183; see there. When Malkhut ascended to Bina in the second constriction, it caused a separation (called a diaphragm) to form on that level between the sefirot above (Keter and Ḥokhma) and those below (Bina, Tiferet and Malkhut).
The sefirot above the diaphragm are those of the "front," meaning more on the "inside" relative to the supernal light. Those below are the "back," meaning on the "outside" relative to the supernal light. Since the Zohar wishes to allude to the combination of Malkhut with Bina, it therefore calls the sefira of Bina by the name of Beria, since before that combination there was no image or form in Bina, even with respect to the recipients, but solely in Malkhut.)