A false promise to reimburse someone cash for buying a product. Originally from the term re-bait which means to lure or trick someone over and over again. In order to make a product seem less expensive, some manufacturers offer a rebate of cash if you buy their product and them follow vague and difficult instructions that involve cutting things out, stapling things together, photocopying, mailing or shipping items and them waiting six months for a check that never comes. If the company really wanted you to save money, they would just have a promotional sale.
See also RIP-OFF, MAIL FRAUD.