In the Book of Mormon, the plates of Nephi, consisting of the large plates of Nephi and the small plates of Nephi, are a portion of the collection of inscribed metal plates which make up the record of the Nephites. This record was later abridged by Mormon and inscribed onto gold plates from which Joseph Smith translated the Book of Mormon.
After Nephi had begun the large plates, he was instructed by the Lord to make another set of plates to record "the ministry and the prophecies, the more plain and precious parts of them." These smaller plates were kept by Nephi's descendants until about 150 BC, when the prophet Amaleki delivered the plates to Benjamin, king of Zarahemla, who "put them with the other plates, which contained records which had been handed down by the kings" (Words of Mormon 1:10). Amaleki's last writing was to state that the small plates were full (Omni 1:30) and from this point there were no further additions to the small plates. Mormon did not abridge the small plates of Nephi, but he did include them in the records he gave to his son Moroni (Words of Mormon 1:6).
The first seven books of the Book of Mormon, from First Nephi to Omni are a translation of the small plates of Nephi.ru:Малые листы Нефия