Very often developers, project managers and business analysts think that the User Interface and User Experience are one and the same. This is a common misconception people say UX or UI, as if they mean the same thing. Even though both are related to the end user’s point of view, they are quite different. The best way to illustrate this is by using the Iceberg analogy. The User Interface is only the tip of the iceberg, it is the most visible part and it is easy to spot. However, as we all know icebergs have 90% of their total mass submerged. Only 10% is visible above water level.
One critical difference between UI and UX is the type of thinking involved. While the UI is concerned how the application looks, e.g. the layout of elements and relative position or size, whitespace etc. the UX design involves asking deeper questions about the problem in order to uncover any hidden assumptions.

UX UI Iceberg

UX UI Iceberg (Adapted from the UX blog}