Block Order

What Does Block Order Mean?
A signficant order placed for sale or purchase of a large number of securities. Block orders are often used by institutional investors.

Also known as a "Block Trade".

Investopedia explains Block Order
Typically, a 10,000 share order (excluding penny stocks) or $200,000 worth of fixed-income securities would consititue a block order. When a trader wants to unload his or her securities quickly they will often sell them at a discount, aptly named a "blockage discount".