What is the difference between UX and UI?

Question

What is UX ? And what is UI? Please, tell me the differences. Is UI a part of UX?

Answer 1

It's like a restaurant.
The utensils, plate, table, chair, that's user interface (which can contribute to experience).
The food, service, ambience, that's user experience.
Update: To put it very simply: The UI is what people use to interact with your product, and the UX is how they feel while they do.

Answer 2

Clearly, there's overlap between these two roles in the academic definition. In my experience,most businesses use the terms UI and UX interchangeably. The definition of the title depends entirely on the company. 
Generally, what they mean is: the UI/UX designer is a person who is responsible for strategizing, organizing, and executing an interface that accomplishes that company's business goals. Depending on the team, this might include any combination of the following deliverables:
User researchOverall strategic direction