No matter how much it has advanced along the way, a website or application still hinges on just one thing: how users perceive it.
Is it easy to use? Is it pleasant to use? Does it give me value? These questions run through the minds of consumers as they interact with your products. Simultaneously, their minds form decisions based on their experience to define if they should use it again or no.
User experience (abbreviated as UX) is how a person feels when interacting with a system. It includes a website, mobile application, desktop software, and any other human/device interaction.