Can you explain what is open and closed book in the book building system?

In an open book building system the merchant banker along with the issuer ensures that the demand for the securities is displayed online on the website of the Stock Exchanges.

Here, the investor can be guided by the movements of the bids during the period in which the bid is kept open. Indian Book building process provides for an open book system.

In the closed book building system, the book is not made public and the bidders will have to take a call on the price at which they intend to make a bid without having any information on the bids submitted by other bidders.