http://www.investopedia.com/terms/b/buyin.asp#axzz2FObjSxdk
Definition of 'Buy-In'
When an investor is forced to repurchase shares because the seller did not deliver the securities in a timely fashion, or did not deliver them at all.
Investopedia explains 'Buy-In'
Those who fail to deliver the securities will be notified with a buy-in notice. Failure to answer the buy-in notice means the broker can buy the securities and deliver them on your behalf. You must then pay back the broker at whatever price.
Definition of 'Sell-Out'
When a broker or investor buying stocks has failed to settle the trade in a timely manner and, as a result, the broker can forcibly sell the securities on the investor's behalf. Investopedia explains 'Sell-Out'
A perfect example of this is when the broker sells a person's stock to meet a margin call.
