This article contains the following statement.
In terms of liquidity detection, traders intend to decipher whether there are large orders existing in a matching engine by sending out small orders (pinging) to seek for large orders. When a small order is filled quickly, there is likely to be a large order behind it.
Am I right to suppose that by pinging the mean difference between the time of sending the order and time of posting it on LOB? Or maybe it's something else?