Definition: Trades greater than or equal to 10,000 shares in size and greater than or equal to $100,000 in value. The exact definition varies, but usually is 20,000 shares, 50,000 shares or 100,000 shares.
Example: 10,000 shares of stock (not including penny stocks) or $200,000 worth of bonds would be considered a block trade. However, in practice block trades are typically much larger as large hedge funds and institutional investors buy and sell huge sums of dollars and shares in block trades via investment banks and other intermediaries virtually on a daily basis.