A tool used to create a quick graphical representation of a finished User Interface without the need to write any code. This tool will commonly have a drag and drop interface allowing a user to arrange UI elements easily.
The most common use of Mockups in software development is to create user interfaces that shows the end user what the software will look like without having to build the software or the underlying functionality. Software UI mockups can range from very simple hand drawn screen layouts, through realistic bitmaps, to semi functional user interfaces developed in a software development tool.