When trading large amounts of stock the lingo changes from simply, "I bought 15 shares of Apple today Bob." Institutions such as mutual funds and hedge funds are typically trading so many shares at once that they tend to stick to whole amount standards, one of which is called a "block" of shares.
So how many shares is a block order? A standard block is 10,000 shares total which for the average investor should make heads spin because 10,000 shares of a stock trading at $50 is $500,000 worth of stock. So, instead of a fund manager saying, "I bought 100,000 shares of XYZ today" they will say instead, "I bought 10 blocks of XYZ today." Try it sometime :twisted:.