In normal orders, the entire order quantity is disclosed to the market. But order with a disclosed quantity allows the investor to disclose only a part of the order to the market.
For example, Mr X wants to buy 100000 shares of a stock at the prevailing market price. If he does not want to disclose his order size to the market, he can set the disclosed quantity to 1000. As soon as his 1000 shares are executed, the next order will automatically be sent to the market. This process repeats until all he has purchased 100000 shares.