Iceberg is an algorithm which similar to how most icebergs visually look very small with most ice hidden beneath, posts small orders into market while holding the balance to optimize price and size of various orders while keeping in synchronization with each tick in the market.Once the previous posted orders are executed they are replaced with the next chunk of orders of the same size as that of the previous one.
Example:
Buy 10000 Nestle Industries at 120.00 showing 100 at a time, good for the day.
The iceberg will place one order with 100 quantity in the market, once all these quantities are traded only then next child order for the same quantity i.e: 100 will be placed in the market.This goes on till all the 10000 quantity has been traded.
You can read more on such execution based algo's here.
Since it is an algo which places order automatically, it is not allowed for retail traders in India, and is typically used by HNI and Institutions who have access to advance dealer terminals.
Disclosed quantity is basically an option that every trader gets while placing an order on how much of the quantity should be visible and how much should be hidden. So if you place an order to buy 100 shares at Rs 1000 with disclosed quantity as 50, the marketwatch will show only 50 to be pending at price of Rs 1000. This can be used by retail traders trading big volumes, if they are worried that placing a big limit order will hamper the order execution. Disclosed quantity is a feature available mainly for equity segment only.