Offers on an order book

An offer is a standing order: “I will trade this much of A for that much of B.” An order book is the list of those offers. A trade happens when two offers cross.

The best offer on the book is a real posted price, not a picture in an ad. If you do not read the rate and the size, you can fill at a worse price than you meant.

You post an offer and it sits until someone takes the other side, you cancel it, or it expires. Takers walk the book from the best price outward. If your order is bigger than the best offer, the rest fills at the next prices. That walk is why “market buy” can cost more than the first number you saw.

Offers can be partially filled. The leftover stays on the book at the same rate until it is done or pulled. Canceling an offer is its own transaction, and it costs a fee like any other.

Real example: the XRP Ledger’s built-in exchange matches offers between XRP and issued tokens, or between two issued tokens. The ledger keeps the book and crosses offers when prices meet. It does not fill in a private back room. Source: Decentralized Exchange.