A more thorough explanation:

A treasury share is a type of stock that a company has issued but then reacquired and either canceled or held. It is also known as treasury stock or reacquired stock. Some states treat such stock as if it is authorized but unissued.

For example, if a company issues 100 shares of stock and then buys back 20 of those shares, those 20 shares become treasury shares. The company can either cancel them or hold onto them for future use.

Treasury shares can be used for a variety of purposes, such as employee stock option plans or to boost earnings per share.