ATi has been added to the NASDAQ-100 stock index. What exactly does this mean? Weren't they already listed on NASDAQ? Glad you asked:

"The NASDAQ-100 Index, founded in 1985, comprises the 100 largest non-financial stocks on the NASDAQ Stock Market and was launched with the NASDAQ Financial-100 Index, which comprise the 100 largest financial stocks on NASDAQ. These indices were originally designed to segment NASDAQ into two major industry groups to support media coverage and to act as benchmarks for financial products such as options, futures, and funds. The NASDAQ-100 is re-ranked each year in December, timed to coincide with the quadruple witch options expiration Friday of the quarter."