If you’re an employee and a customer directly or indirectly gives you extra money in addition to the amount they pay for services or a product, that’s considered a tip. For example, if you’ were a waiter/waitress in a restaurant, a customer will pay the bill and decided to leave you $20 cash on the table for your awesome service.
Generally, if you receive more than $20 a month in cash tips, you must report them to your employer. The key word here is “cash” which includes tips a customer leaves on a credit/debit card charge. Unreported tip income occurs when you don’t have to report the cash tips you made to your employer because it was less than $20 total for the month and/or you received non-cash tips such as a tickets to an event or other items of value.