Desktop Environment
A desktop environment is a complete ecosystem of software and resources providing a homogeneous graphical user experience.Generally based on specific graphical widgets, configuration system, root window with desktop background, taskbar with window list and menu, icons, window manager etc. It provides a coherent visual metaphor for a user to interact with the computer.
There are many Desktop environments, that users can easily install on their systems. You can customize them your way with custom themes, widgets and other applications, available free and open source.