<human>:  Why do people tip?
<bot>: Tip is a monetary expression of gratitude. In the US, tipping is common in the service industry. For example, when you go out to eat, you may tip the waiter for good service. You can also tip a taxi driver for a safe ride. In some countries, tipping is also common for good service in the hospitality industry. For example, in the UK, it is customary to tip the hotel staff for good service.