In the forex market, the Top Of Book refers to the highest bid and lowest ask prices that are currently available for a particular currency pair. The bid price is the highest price that a buyer is willing to pay for a currency, while the ask price is the lowest price that a seller is willing to accept for a currency. The difference between the bid and ask prices is known as the bid-ask spread.The top of book is considered to be the most liquid and reliable prices available in the market, as they are the prices that are available to the public and reflect the most current market conditions. This information is typically displayed on trading platforms and can be used by traders to make informed buying and selling decisions.It is important to note that the top of book prices are not always the same as the executed prices, as the prices may change quickly and the bid-ask spread may fluctuate. Additionally, large orders can also affect the top of book prices, which can cause them to change rapidly.In summary, in the forex market, the top of book refers to the highest bid and lowest ask prices that are currently available for a particular currency pair. The top of book prices are considered to be the most liquid and reliable prices available in the market and can be used by traders to make informed buying and selling decisions. However, it's important to note that the top of book prices are not always the same as the executed prices, as the prices may change quickly and the bid-ask spread may fluctuate.