Pachinko (パチンコ) is a mixture of slot machine and pinball. The player is quite passive while playing pachinko and mainly controls the speed with which many small steel balls are thrown into the machine. Pachinko machines can be found in pachinko parlors across the country, which can be recognize by their bright and colorful exteriors and noisy interiors.
Balls can be purchased at each machine using cash or prepaid cards. When propelled into the machine, most balls will simply fall down the machine and disappear, but a few find their way into special holes that activate a kind of slot machine. When this happens (and this is relatively rare), you can win countless new balls. Note that if you play only with a few hundred yen, your balls are likely to all disappear within just a couple of minutes.
The balls can be exchanged at any time into goods at the parlor's gift shop. But you can also bypass the law that prohibits gambling in Japan by exchanging the balls first into some special goods and then exchange the special goods for cash at a small window just outside the parlor.