black rain; radioactive fallout rain
Refers to the heavily polluted, radioactive rain that fell after the atomic bombing of Hiroshima (and sometimes other nuclear explosions). The term is strongly associated with that historical event.
After the black rain fell on Hiroshima, many people were exposed to radiation.
It is important to pass on the experiences of the black rain.
Compound of 黒い (black) and 雨 (rain). The term gained its specific meaning from the radioactive soot-laden rain that followed the Hiroshima atomic bombing.