Great question! In the context of a restaurant, leaving a tip is leaving a little extra money for the person who served you your food (the waiter/waitress/server). You can do this physically, by leaving some money on the table (this is why it is "leaving" a tip). Most of the time, however, tipping is now done through a debit machine. In Canada and most places in America, waiters make less money in their hourly pay than other people do. Tipping is an important social custom in North America. In Canada, we usually tip 15%-20% of the total we pay for the food. If we are unhappy with the food or service, we might tip 10%, or even 5%. In a Canadian (and I assume American) restaurant, choosing not to tip sends a very strong message. It means you were very, very unhappy with some aspect of your meal.