What is 'rev hang'?
'Rev hang' is the common term for when the engine speed does not fall immediately when shifting. It only affects manual transmission vehicles. Some models do not have 'rev hang', in others vehicles it is noticeable when shifting.
How do I reduce 'rev hang'?
There are several things to check in order to reduce rev hang. Note that not all vehicles may have these options - if the options are missing, then it could be that those vehicles do not have the ECU behaviour which causes rev hang.
Overrun throttle
Uncheck Parameter -> Throttle -> Overrun throttle opening enabled.
This will shut the throttle plate quicker when the throttle pedal is released. In turbo vehicles like the 2016+ 1.5T Civic, enabling the main cruise control button will cause the throttle to go back to stock behavior.
Overrun Fuel Cut Delay
Reduce the overrun fuel cut delay values in the table at Parameters -> Fuel. This table is by gear, suggested values are 20-50 ms.
This will shut the injectors off quicker when the throttle is closed.
Note that your vehicle must be well tuned as well. Excessive closed loop fuel trims give similar symptoms to rev hang.