Hidden orders are usually larger trade orders which are kept out of the public order book by the trade broker. Keeping out of public orders books is done to limit the mostly psychological impact the trade may have on other market participants. As traders can see the positions taken by other traders, it may lead them to modify their own order at an unfavorable rate. Thus, Hidden Orders allow traders to maintain anonymity in the market. Hidden Orders can also be called "Dark Pool Orders."
Pros: Anonymity
Cons: May limit liquidity access in fragmented markets.
Hidden Orders pay taker fees.