A company's board has decided to increase the number of outstanding shares in the company by issuing new shares to existing shareholders in a set proportion. This is known as a:

A tender offer is an offer made by a company to buy back its own shares from existing shareholders, often at a premium over the market price. This option reduces the number of outstanding shares rather than increasing them, as it involves repurchasing shares instead of issuing new ones, which does not fit the description of a rights offering.

In a rights offering, existing shareholders are given the opportunity to purchase additional shares at a predetermined price, usually based on their current ownership percentage. This action increases the number of outstanding shares while allowing shareholders to maintain their relative ownership in the company.

A stock buyback occurs when a company repurchases its own shares from the market, effectively reducing the number of outstanding shares. This action typically aims to boost the stock price and return value to shareholders but does not involve issuing new shares to existing shareholders in any form.