Short answer: In a restaurant, “86” means an item is out of stock and can no longer be ordered, as in “86 the salmon.” It can also mean remove something from an order (“86 the onions”) or, less often, refuse service to a guest. The origin of the term is uncertain; there are several popular theories but no confirmed source.
Keep the 86 list where every server can see it.
How 86 is used
Sold out: “86 the short rib” means no more short rib tonight.
Remove from an order: “Burger, 86 the pickles.”
Remove a person: in bars, being “86’d” can mean a guest is no longer served.
Manage the 86 list
The kitchen calls the 86 as soon as an item runs out.
The expo or manager updates the POS so servers cannot ring it in.
Servers are told before pre-shift or right away during service.