Issued shares equal outstanding-shares plus treasury-stock. The distinction matters because treasury shares do not vote, do not receive a dividend, and are not counted in per-share figures, but they can be re-issued without a new authorization.
When you read a filing, check which number the company is quoting. Marketing materials often show outstanding; the charter section shows issued against authorized-shares.
Example: a company issued 300M shares over its life and repurchased 40M that sit in treasury. Issued is 300M, outstanding is 260M, and earnings per share is computed on roughly 260M, not 300M.
Related: authorized-shares, outstanding-shares, treasury-stock, eps