To sell more of a product or service than can be supplied or delivered. The airline oversold the flight, leaving several passengers without seats.
To promote or praise something excessively, often leading to unrealistic expectations. The marketing team oversold the new product, leading to customer disappointment when it didn't meet the hype.
(Finance) To sell a security or asset so heavily that its price falls to a level considered below its intrinsic value. During the market crash, traders oversold tech shares, pushing prices to decade lows.