Sometimes an investor or a company looking to buy back its own shares wants to buy a larger block of shares in one go than the market can normally accommodate. A tender offer involves setting a fixed price at which you are prepared to acquire up to a fixed number of shares. Shareholders are given some time to decide whether to accept the tender offer or not.
If more shares are tendered to the offer by shareholders than the buyer has agreed to purchase, selling shareholders may be scaled back. In these cases the tender offer is said to be oversubscribed.