Authorised Shares：公司被授权可以发行的股份；

Issued Shares：公司实际发行的股份；

Outstanding Shares：公司股东持有的股份。

一般来讲，Issued Shares＝Outstanding Shares，在发生Share Repurchase的情况下，Issued Shares大于Outstanding Shares。

Share Purchse：是指公司从股东手里回购股份，回购后，公司自己持有自己的股份，不清楚这种股份的专有名词，姑且称这种股份为Repurchased Shares。这种情况下，Issued Shares＝Outstanding Shares＋Repurchased Shares。公司可以随时卖出Repurchased Shares，而不需履行发行股份的程序。

引用某网站对Outstanding Shares的解释：

Outstanding Shares（www.investopedia.com）

Stock currently held by investors, including restricted shares owned by the company's officers and insiders, as well as those held by the public. Shares that have been repurchased by the company are not considered outstanding stock.

Also referred to as "issued and outstanding" if all repurchased shares have been retired.