Merger: cydy company and other company merge into one company (let’s say: new company). Shareholders of cydy and shareholder of other comoany get shares of new company in return.

BO: other company buys the shares from Cydy from cydy shareholders. Cydy shareholders get cash (and/or share in other company) in return.

Partner: cydy shareholders remain cydy shareholders. Cydy company has a partnership with other company and they share profits.

In short and simplified.