The period of history ushered in by Joseph Smith. Mormons believe that after the original twelve apostles died, a Great Apostasy occurred. It was a period of spiritual darkness where people had lost the “fulness of the gospel truth.” They believe the priesthood was also gone from the earth. It was not until Heavenly Father and Jesus Christ appeared to a young Joseph Smith in the early 19th century that the fulness of the gospel and the priesthood were restored. Mormons believe the lost teachings can be found in LDS scriptures. For these reasons, the LDS Church considers itself the only true Christian church.
Dictionary of "Mormonese"
Stop talking past each other. Gain a better understanding of the words that are unique to Mormonism and the differences of shared terms between Mormonism and Christianity.