Issued Shares
Shares that have actually been distributed to shareholders, from the authorized share pool.
Definition
Issued shares are shares that have been allocated to shareholders, including both outstanding shares (held by current shareholders) and any treasury shares (shares the company has repurchased). This is a subset of authorized shares. The difference between authorized and issued shares represents the company's capacity to issue more equity without amending its charter.
Why it matters
Knowing the issued vs. authorized share count helps you understand how much room the company has to grant more options or sell more shares without needing shareholder approval to increase the authorized count.
Example
A company has 20M authorized shares and 12M issued shares. Of those 12M, 11.5M are outstanding and 500K are treasury shares. The company can issue 8M more shares before needing to increase the authorized count.