In short, a hopper is the payout unit of certain slot machines. This means that a hopper is always used when the Player has won a prize. So if a player plays a slot with five paylines and a Bet per line of 0.10 euros, then the total bet is 0.50 euros. If a win of, for example, 4.00 euros is won, then the payout is made via the so-called hopper.
The hopper automatically counts the win amount from the corresponding payout units and then pays out the win to the player. In addition to the classic hopper, which usually only pays out coins, there are now also so-called "banknote recyclers". This means that banknotes are also paid out as a win on such a machine. Of course, there is a hopper logically only in the stationary slot machines. Since there are no cash payouts in online casinos and online gaming arcades, no hopper is needed here either.
Nowadays, however, hoppers are rarely used even in land-based casinos. This is because the payout of wins here is usually done via a Cashout ticket. So the software simply prints out a barcode with the winning amount. The cash is then paid out by the supervisory staff by hand.