In code, an action is simply a plain JavaScript object having a type key:

const incrementAction = {
  type: 'counter/increment'
};

Additional keys can be added to represent information or data related to the action:

const incrementAction = {
  type: 'counter/increment',
  amount: 7
};

The types are named in a specific way by convention. The general syntax is domain/eventName. In this above case, it is counter/increment.

The domain represents the category of the action, while the eventName represents the event itself.