What is all this user stuff?
Everything around us is designed to be used, in order to serve in a specific need. Products, software, architecture, services, you name it: we create our own world to make it a better place for ourselves.
How we use a product (I am just gonna say product now for all the above) determine if, when and how we reach the goals that it was intended to. Good design is therefore effective, efficient and satisfactory (the three elements of Usability).
But we humans are no machines, we strongly bond with the products around us (do you love or hate your car, shoes, kitchenware or smartphone?). The way we feel about our products before, during and after product use determine how we experience the product, the people connected to it and, ultimately, the brand that put it in the market.
Notable is that these experiences are in large part influenced by the context in which we use (or have used) the product (are you in a hurry or have you just made a promotion?). These three elements contribute to the User Experience of product use.