Authorized Shares means the total number of shares of stock the company is authorized to issue by its Articles of Incorporation. In contrast, Issued Shares means the number of shares of stock actually issued by the corporation to shareholders. Treasury Shares means Issued Shares held by the corporation, but note that Treasury Shares are typically held only by publicly traded companies.

A note about terminology: California corporate law refers to stockholders as shareholders while Delaware corporate law refers to stockholders. The meaning is the same.