I think in this case he intends serialization to mean the transformation of an action to a medium that can be sent to another system or application. An action can be serialized into JSON and then returned as an object to another system or application that can then read it, and use it. In this case it's temporarily stored as a JSON object, but for the purposes of communication.
Storing it for later means just that. Write it to an object and persist it somewhere. Local storage in the browser or an object based DB or wherever. Then you can read it back later and use it. Both can be powerful techniques.