Tab (open check)
A tab is an open bill that collects everything a table or guest orders during a visit, paid once at the end instead of after each order.
Tabs are common in bars and in sit-down restaurants where guests order in rounds: drinks first, then food, then dessert. Each round is added to the same tab, and the guest settles the total when they leave. Once it is printed, the tab is the bill, also called the check.
Some bars open tabs under a guest's name, sometimes holding a card until the tab is closed. Restaurants more often tie the tab to a table, so everyone at that table shares one bill unless they ask to split it.
The risk with tabs is a bill that is never closed, or an item that never reaches it. A POS that adds each confirmed round to the tab, and shows every open tab to the cashier, keeps both under control.
Example
At a rooftop bar in Jhamsikhel, a group orders two beers, then a plate of chicken chilli an hour later, then another round. Each order goes on table 3's tab, and they pay one bill at the end of the night.
KalasOS specifics
In KalasOS, a tab is the table's open check. With table service, each Confirm Order adds a new round to it until the check is billed. There are no named tabs: a check belongs to a table or to a takeaway order. With split billing on, a waiter can split a table's items across several checks. In counter service, every order is its own check and cannot be added to later.