From a React POV:
Store: A single place to store information (Like a book someone else is writing for you)
Action: Little piece of message you send (dispatch) to the store (Requests to the writer)
Reducer: Logic to interpret the message and edit the store (How the writer should act according to the requests)
Middleware: They have access to what's going on (Like someone who is listening to all the requests you sent to the writer)
I hope that's basic enough...
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