Trading glossary · practical definition
What is order book depth?
The visible quantity available at bid and ask prices away from the mid-price.
Order book depth in plain English
The visible quantity available at bid and ask prices away from the mid-price.
Depth helps estimate price impact but can change or be cancelled before execution.
Practical example
Two venues can show the same spread while one has much more size within 10 basis points.
Common mistake
Treating displayed liquidity as guaranteed.
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