Tronc is a term most often used in brick-and-mortar casinos; it refers to the box used by players to tip the dealer at casino table games. Players often tip the croupier for dealing them a good hand or simply out of goodwill, which is an excellent way for dealers to make some additional cash.
The contents of the tronc are split either between dealers operating at the same table or between all the dealers working in the casino at the end of the shift. In some cases, casinos use a seniority system, meaning that dealers who have been working in a casino for a while get a bigger cut of the money made from tips.
Regardless of the details or how the money is split, the meaning of tronc is the same in all casinos.