Gateway
1. A Gateway is a particular webpage designed to attract internet users and search engines to a particular website.
2. A gateway is an intermediary which functions as a server on behalf of another server with the aim of supplying resources or resource manifestations from the original server.
GUI
A Graphical user interface (GUI) allows users to interact with computers using an administration interface rather than text commands. GUI generally has three major components: a windowing system, an imaging model, and an application program interface (API). The windowing system generates the windows, menus, and dialog boxes that display on the screen. The imaging model delineates the fonts and graphics that appear on the screen. Lastly, the API is the means by which users indicate how and what windows and graphics appear on the screen.