UI = User Interface

The acronym “UI” stands for User Interface.  It’s usually used in the context of computer software to talk about the on screen display and how the user interacts with the software.  For modern operating systems, most provide a graphical user interface (GUI) that provides push buttons, check boxes, etc… All the stuff you’re used to if you use a Windows machine or a Mac and even most flavors of Linux.  Most modern cell phones now have GUIs too.  Not all UIs are slick GUIs though.  Prior to Windows and Mac were console applications that provided only text displays and usually presented the user with a list of options in a “menu” of choices with numbers beside each option and a flashing cursor waiting for the user to type the number of the option they wanted.  User interfaces aren’t required to be “visual” either.  For example, your cell phone or your GPS may have voice recognition and voice playback.  That is a form of a user interface (UI) that is audio based.