A sign-up bonus is a promotion offered by a credit card issuer to entice you to apply for a card and begin using it regularly. The term "sign-up bonus" is a bit of a misnomer because in most cases you don't get the bonus just for signing up; you have to earn it by spending money. That's why some issuers use terms like "bonus offer," "welcome offer" or "new cardholder offer" rather than sign-up bonus.
Sign-up bonuses give you a lump sum of cash back or a large number of points or miles if you spend a certain amount using the card in a specified time period, usually the first few months after opening the account. After you complete the required spending, the bonus is applied to your account. Separate from that lump-sum bonus, or in addition to it, some credit card sign-up offers include a more valuable rewards structure for a limited time (such as a higher rewards rate in the first year) or a special perk for new cardholders (such as free hotel nights or one-time discounts).