What "Connection_Dropped_List_Full" in IIS Httperr log refers to?

I can see from official description on (https://support.microsoft.com/en-us/help/820729/error-logging-in-http-apis) that it refers to The list of dropped connections between clients and the server is full. Specific to Windows Vista and later versions and to Windows Server 2008 and later versions. This explanation does not really make sense since there is no information what exactly that list is and how do you monitor it or configure it. This is not related to application queue being full since that one is presented as separate error message in the same error log as QueueFull error. Anybody has any insider details what that error specifically means and how it can be configured or monitored