Surah 99. Az-Zalzalah, Ayah 2

I.e., all that was hitherto hidden in it, including the bodies - or the remnants - of the dead.

 lit., burdens (i.e., treasures and dead bodies).

An earthquake, if accompanied by a volcanic eruption, throws up enormous boulders and lava from beneath the crust of the earth. They are thrown up as if they were a burden to the Earth personified. They may be all kinds of minerals, or treasures buried for secrecy. So in the great and final Convulsion, the dead who had been buried and forgotten will rise; and will be brought to the light of day, and justice will be done in the full glare of absolute Truth.