The abbreviations UI, UX, CX and HX are used in design (especially web and app design) and are often confused or even misused.
UI = User Interface is widely used as it describes the design of the website (or app or device) as that place where the human interacts with the machine. This includes the flow of the product through wireframes elements such as graphic design colors and lines but also the research aspects of UX.
UX = User eXperience (also called UE, just to further confuse things) is a person’s emotions and attitudes about using a particular product, system or service.
CX = Customer Experience is more of a term used in the commerce aspects of using a website and can more widely apply to offline experiences. The overlap is the parts of the customer “journey.”
HX = Human Experience is a new term I have seen but it doesn’t even have a Wikipedia entry – which tells you something about its limited usage.
The terms certainly have some overlap and perhaps not all of them are needed. HX seems to be an umbrella term for what a customer experiences when they use your website – which makes it sound like a synonym for CX. Not all “users” are customers (in the sense of making purchases) and so those terms emerged.
The links above go to the Wikipedia entries and are a good starting place, as is the video below.