What is a nuclear eclipse?

Answer 1

The detonation of an atomic fission weapon at-or-near ground level draws vast quantities of material into the atmosphere. In the event of multiple such detonations, so much dust can be drawn into the atmosphere that the sun is effectively blocked from view of the planet's surface; a nuclear eclipse. In a theoretical end-of-world scenario, if the sun becomes eclipsed for a prolonged duration, blocking the light and heat of the sun from the surface, this may become what is called a Nuclear Winter.

Answer 2

A nuclear eclipse is not a recognized astronomical event. It may be a misuse or misunderstanding of terms, as "nuclear" typically refers to atomic or nuclear energy, while an eclipse is when one celestial body is obscured by another.