USER INTERFACE : In computer science and human-computer interaction, the user interface (of a computer program) refers to the graphical, textual and auditory information the program presents to the user. The user employs several control sequences (such as keystrokes with the computer keyboard, movements of the computer mouse, or selections with the touchscreen) to control the program.Generally, the goal of user interface design is to produce a user interface which makes it easy (selfexplanatory), efficient, and enjoyable (user-friendly) to operate a machine in the way which produces the desired result. This generally means that the operator needs to provide minimal input to achieve the desired output, and also that the machine minimizes undesired outputs to the human.
There exist several types of user interfaces. We here give you just two examples: Command-Line Interface (CLI): The user provides the input by typing a command string with the computer keyboard and the system provides output by printing text on the computer monitor.
Graphical User Interface (GUI): The use of pictures rather than just words to represent the input and output of a program (Linux junkies). Input is accepted via devices such as keyboard and mouse.