The dead declare to Babylon that it is now dead. It’s glory is dead and brought to the grave, where it might have memory, but certainly has no reality. The worms are the reference of the fate of the dead, to be consumed by the worms to lose even what little substance it had.
Variant: The Book of Mormon contains an addition to the KJV text (noted in brackets):
Isa. 14:11
11 Thy pomp is brought down to the grave, and the noise of thy viols [is not heard]: the worm is spread under thee, and the worms cover thee.
There is no change in meaning, only a clarification of the reading. The NIV also improves the reading of this passage, but does so with a different structure:
All your pomp has been brought down to the grave,
Along with the noise of your harps;
The problem comes from the Hebrew assumed parallelism of the phrases for the pomp and harps. The “and” is italicized in the KJV, indicating that it is a translator’s solution to a grammatical/literary assumption in the Hebrew. The NIV solves that assumption with another addition; “along with.” The Book of Mormon is just another mode of making sense of the passage in English. As Tvedtnes notes, there is no manuscript tradition supporting this reading (Tvedtnes, 1981, p. 58.)