> ## Documentation Index
> Fetch the complete documentation index at: https://docs.xo.market/llms.txt
> Use this file to discover all available pages before exploring further.

# Order book basics

> Bids, asks, spread, depth, slippage — and why your available balance can look low.

## The vocabulary

| Term      | What it means                                                                                             |
| --------- | --------------------------------------------------------------------------------------------------------- |
| Bid       | An order offering to buy shares at a price.                                                               |
| Ask       | An order offering to sell shares at a price.                                                              |
| Best bid  | The highest current buy price.                                                                            |
| Best ask  | The lowest current sell price.                                                                            |
| Spread    | The gap between the best bid and the best ask.                                                            |
| Depth     | How many shares are available at each price level.                                                        |
| Liquidity | How easily a position can trade without walking through many price levels.                                |
| Slippage  | The difference between the first displayed price and your average execution price across the filled size. |

## Reading depth before you size an order

The best price applies only to the shares available at that price. A larger order walks up through worse levels, and your average price is what you actually pay.

Before sizing up, look at how much depth sits within a price range you'd accept. If the book thins out two levels in, that is your real capacity — not the headline quote.

## Reserved cash and shares

Resting orders hold funds:

* an open **buy** reserves cash equal to its cost
* an open **sell** reserves the shares it would deliver

Reserved amounts are unavailable for anything else until the order fills or you cancel it. If a new buy is rejected for insufficient funds while your wallet shows a balance, check open orders first.

## Orders can be cancelled for you

A resting order can be cancelled without you asking. A **paused** market rejects new orders but keeps existing ones, ready to return to Active. **Resolved**, **Voided** and **Closed** are terminal and cancel resting orders.

There are other conditions under which the book cancels resting orders — integrators should read [Auto-cancellation](/guides/auto-cancellation).

Resolved and voided positions can become claimable. See [How markets resolve](/product/portfolio/how-markets-resolve).