pachinko ball
Refers to the small steel balls used as game pieces in pachinko parlors.
See also: パチンコ
パチンコ玉をたくさん集めて景品と交換した。
I collected a lot of pachinko balls and exchanged them for prizes.
Compound of パチンコ (pachinko, the game) and 玉 (ball). The word パチンコ is of Japanese origin, likely onomatopoeic.