Silver mining is a term used in brick-and-mortar casinos that refers to the practice of walking from one slot machine to another in the hope of finding coins at unattended slot machines. Sometimes, people walk from one machine to another after the players have left, hoping that someone has forgotten a coin or two after receiving a payout.
The term is also known as slot walking, which is a playful way to refer to sleepwalking since people who practice silver mining appear to be aimlessly walking from one machine to another as if they were asleep.
While knowing what silver mining and slot walking stand for may prove useful, it is more important to remember that silver mining is a thing. Therefore, if you end up playing slot machines in a land-based casino, make sure to keep an eye on your coins and never leave them unattended, as you might come back to a smaller number of coins after leaving your seat.