Here are two well used definitions of the term 'buyout':
The purchase by the managment of a company of its shares, making the management the owner of the company. Many buyouts use borrowed money - they're what is known as leveraged .
The purchase by the company itself of its shares held by the public, taking the company off the stockmarket and making it a private company.
Buyout can be used to describe the purchase of at least a controlling interest in a company's shares.