TLDR:
Issued shares are the total number of shares that a company has actually issued to shareholders from its pool of authorized shares, including both outstanding shares and treasury shares held by the company.
Managing Issued Shares Over Time
As a startup grows through multiple funding rounds, the number of issued shares increases with each new equity issuance — new investor rounds, option exercises, and warrant conversions all add to the issued share count. Managing the issued share count relative to the authorized share count is an ongoing governance responsibility: when issued shares approach the authorized ceiling, the company must approve an increase in authorized shares (typically requiring shareholder approval). Well-run startups maintain a ‘reserve’ of authorized but unissued shares to accommodate future equity needs without emergency governance actions.