Slippage: This occurs on any financial market. It is described as the difference between the price requested by a trader for the execution of a trade and the price at which the order was filled by a broker. It can occur regardless of order type (Market execution, Buy limit, Sell limit…etc), rules of an exchange (NASDAQ, NYSE…etc) or the broker.
If the trade/order was not executed at the price requested and a worse price was provided by the broker, this is described as Negative Slippage and is in favor of the broker, however; if the opposite occurs i.e. the trade/order is executed at a better price than requested by the trader, then it is referred to as Positive Slippage and is in favor of the trader.
Slippage occurs mainly due to the latency i.e. the time delay between the trader submitting his/her order and when the broker’s server receives and processes the order. Internet speed, Internet quality and geographic distances between servers all adds to this latency problem, add on top of that the fast nature of financial markets.
If a broker only provides negative Slippage most of the time this is referred to as Asymmetrical Slippage and they can be fined by regulatory bodies such as the National Futures Association (NFA) in the US. If Slippage is to occur, it must be Symmetrical i.e. both negative and positive Slippage must be passed on to the trader/client.
Requote: This is similar to and bears all the same characteristics of Slippage but instead the broker just filling your order at a negative or positive price, the broker would send you a notification via your trading platform with the option to either execute the trade at a positive or negative price rate than the price rate you requested.